Old/cached packages are still installed during the build

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We have the following in our Aptfile:

libcairo2 libcairo-gobject2 libxt6 libsm6 libice6 libgtk-3-0 firefox vim

We've just noticed that, during the build, old versions (from previous builds) are still getting installed.

This doesn't impact the dyno size as the new version overwrites the old one, but still, it increases the time of the build, and with time (and more newer versions) it could increase it even more.

Notice the multiple firefox, glib-networking, etc:

remote: -----> Installing adwaita-icon-theme_3.28.0-1ubuntu1_all.deb
remote: -----> Installing at-spi2-core_2.28.0-1_amd64.deb
remote: -----> Installing dconf-gsettings-backend_0.26.0-2ubuntu3_amd64.deb
remote: -----> Installing dconf-service_0.26.0-2ubuntu3_amd64.deb
remote: -----> Installing firefox_73.0.1+build1-0ubuntu0.18.04.1_amd64.deb
remote: -----> Installing firefox_74.0+build3-0ubuntu0.18.04.1_amd64.deb
remote: -----> Installing firefox_78.0.1+build1-0ubuntu0.18.04.1_amd64.deb
remote: -----> Installing glib-networking_2.56.0-1_amd64.deb
remote: -----> Installing glib-networking_2.56.0-1ubuntu0.1_amd64.deb
remote: -----> Installing glib-networking-common_2.56.0-1_all.deb
remote: -----> Installing glib-networking-common_2.56.0-1ubuntu0.1_all.deb
remote: -----> Installing glib-networking-services_2.56.0-1_amd64.deb
remote: -----> Installing glib-networking-services_2.56.0-1ubuntu0.1_amd64.deb
remote: -----> Installing gsettings-desktop-schemas_3.28.0-1ubuntu1_all.deb
remote: -----> Installing gtk-update-icon-cache_3.22.30-1ubuntu4_amd64.deb
remote: -----> Installing humanity-icon-theme_0.6.15_all.deb
remote: -----> Installing libasound2_1.1.3-5ubuntu0.2_amd64.deb
remote: -----> Installing libasound2_1.1.3-5ubuntu0.5_amd64.deb
remote: -----> Installing libasound2-data_1.1.3-5ubuntu0.2_all.deb
remote: -----> Installing libasound2-data_1.1.3-5ubuntu0.5_all.deb
remote: -----> Installing libatk1.0-0_2.28.1-1_amd64.deb
remote: -----> Installing libatk1.0-data_2.28.1-1_all.deb
remote: -----> Installing libatk-bridge2.0-0_2.26.2-1_amd64.deb
remote: -----> Installing libatspi2.0-0_2.28.0-1_amd64.deb
remote: -----> Installing libcairo2_1.15.10-2ubuntu0.1_amd64.deb
remote: -----> Installing libcairo-gobject2_1.15.10-2ubuntu0.1_amd64.deb
remote: -----> Installing libcanberra0_0.30-5ubuntu1_amd64.deb
remote: -----> Installing libcolord2_1.3.3-2build1_amd64.deb
remote: -----> Installing libdbus-glib-1-2_0.110-2_amd64.deb
remote: -----> Installing libdbusmenu-glib4_16.04.1+18.04.20171206-0ubuntu2_amd64.deb
remote: -----> Installing libdbusmenu-gtk3-4_16.04.1+18.04.20171206-0ubuntu2_amd64.deb
remote: -----> Installing libdconf1_0.26.0-2ubuntu3_amd64.deb
remote: -----> Installing libepoxy0_1.4.3-1_amd64.deb
remote: -----> Installing libgpm2_1.20.7-5_amd64.deb
remote: -----> Installing libgtk-3-0_3.22.30-1ubuntu4_amd64.deb
remote: -----> Installing libgtk-3-bin_3.22.30-1ubuntu4_amd64.deb
remote: -----> Installing libgtk-3-common_3.22.30-1ubuntu4_all.deb
remote: -----> Installing libice6_2%3a1.0.9-2_amd64.deb
remote: -----> Installing libjson-glib-1.0-0_1.4.2-3_amd64.deb
remote: -----> Installing libjson-glib-1.0-0_1.4.2-3ubuntu0.18.04.1_amd64.deb
remote: -----> Installing libjson-glib-1.0-common_1.4.2-3_all.deb
remote: -----> Installing libjson-glib-1.0-common_1.4.2-3ubuntu0.18.04.1_all.deb
remote: -----> Installing libogg0_1.3.2-1_amd64.deb
remote: -----> Installing libproxy1v5_0.4.15-1_amd64.deb
remote: -----> Installing libpython3.6_3.6.9-1~18.04_amd64.deb
remote: -----> Installing libpython3.6_3.6.9-1~18.04ubuntu1_amd64.deb
remote: -----> Installing librest-0.7-0_0.8.0-2_amd64.deb
remote: -----> Installing libsm6_2%3a1.2.2-1_amd64.deb
remote: -----> Installing libsoup2.4-1_2.62.1-1ubuntu0.4_amd64.deb
remote: -----> Installing libsoup-gnome2.4-1_2.62.1-1ubuntu0.4_amd64.deb
remote: -----> Installing libstartup-notification0_0.12-5_amd64.deb
remote: -----> Installing libtdb1_1.3.15-2_amd64.deb
remote: -----> Installing libvorbis0a_1.3.5-4.2_amd64.deb
remote: -----> Installing libvorbisfile3_1.3.5-4.2_amd64.deb
remote: -----> Installing libwayland-client0_1.16.0-1ubuntu1.1~18.04.3_amd64.deb
remote: -----> Installing libwayland-cursor0_1.16.0-1ubuntu1.1~18.04.3_amd64.deb
remote: -----> Installing libwayland-egl1_1.16.0-1ubuntu1.1~18.04.3_amd64.deb
remote: -----> Installing libx11-xcb1_2%3a1.6.4-3ubuntu0.2_amd64.deb
remote: -----> Installing libxcb-util1_0.4.0-0ubuntu3_amd64.deb
remote: -----> Installing libxcomposite1_1%3a0.4.4-2_amd64.deb
remote: -----> Installing libxcursor1_1%3a1.1.15-1_amd64.deb
remote: -----> Installing libxdamage1_1%3a1.1.4-3_amd64.deb
remote: -----> Installing libxfixes3_1%3a5.0.3-1_amd64.deb
remote: -----> Installing libxi6_2%3a1.7.9-1_amd64.deb
remote: -----> Installing libxinerama1_2%3a1.1.3-1_amd64.deb
remote: -----> Installing libxkbcommon0_0.8.2-1~ubuntu18.04.1_amd64.deb
remote: -----> Installing libxrandr2_2%3a1.5.1-1_amd64.deb
remote: -----> Installing libxt6_1%3a1.1.5-1_amd64.deb
remote: -----> Installing libxtst6_2%3a1.2.3-1_amd64.deb
remote: -----> Installing sound-theme-freedesktop_0.8-2ubuntu1_all.deb
remote: -----> Installing ubuntu-mono_16.10+18.04.20181005-0ubuntu1_all.deb
remote: -----> Installing vim_2%3a8.0.1453-1ubuntu1.1_amd64.deb
remote: -----> Installing vim_2%3a8.0.1453-1ubuntu1.3_amd64.deb
remote: -----> Installing vim-common_2%3a8.0.1453-1ubuntu1.1_all.deb
remote: -----> Installing vim-common_2%3a8.0.1453-1ubuntu1.3_all.deb
remote: -----> Installing vim-runtime_2%3a8.0.1453-1ubuntu1.1_all.deb
remote: -----> Installing vim-runtime_2%3a8.0.1453-1ubuntu1.3_all.deb
remote: -----> Installing xkb-data_2.23.1-1ubuntu1.18.04.1_all.deb
remote: -----> Installing xul-ext-ubufox_3.4-0ubuntu1.17.10.1_all.deb
remote: -----> Installing xxd_2%3a8.0.1453-1ubuntu1.1_amd64.deb
remote: -----> Installing xxd_2%3a8.0.1453-1ubuntu1.3_amd64.deb

> firefox -V

Mozilla Firefox 78.0.1

> which firefox

/app/.apt/usr/bin/firefox

> ls /app/.apt/usr/bin/

broadwayd
firefox
gtk-builder-tool
gtk-launch
gtk-query-settings
gtk-update-icon-cache
helpztags
vim.basic
vimtutor
xxd

It could be related with #61 / #62