Staged package dedup

[simondeziel]

Stop priming binaries that are already available in the base/core snap. See https://snapcraft.io/docs/build-and-staging-dependencies#heading--filtering for the explanation.

In the case of vim and for the 5.0/stable channel, this would have saved us from using a known vulnerable vim version:

$ grep vim-tiny /snap/core20/current/usr/share/snappy/dpkg.list 
ii  vim-tiny                       2:8.1.2269-1ubuntu5.15       amd64        Vi IMproved - enhanced vi editor - compact version

$ grep '^- vim-tiny' /snap/lxd/current/snap/manifest.yaml 
- vim-tiny=2:8.1.2269-1ubuntu5.11

In the above, core20 ships ... .15 while the 5.0/stable one has ... .11.

The situation with differs for latest/stable as our snap's vim is ahead of what core22 provides:

$ grep vim-tiny /snap/core22/current/usr/share/snappy/dpkg.list 
ii  vim-tiny                       2:8.2.3995-1ubuntu2.9                   amd64        Vi IMproved - enhanced vi editor - compact version

$ grep '^- vim-tiny' /snap/lxd/current/snap/manifest.yaml 
- vim-tiny=2:8.2.3995-1ubuntu2.13

Even then, I think we should rely on what's provided by the base/core snap so that another team is responsible for that "shared infrastructure bit".

[simondeziel]

Superseded by #237