Revert "Set useradd default shell to bash"

This reverts commit 554cfdd.
Strange behaviour: useradd creates user without a shell which defaults
to /bin/sh.

builder/chroot-script.sh

@@ -178,9 +178,6 @@ proc /proc proc defaults 0 0
 /dev/mmcblk0p2 / ext4 defaults,noatime 0 1
 " > /etc/fstab
 
-# Fix default shell for new users created with useradd
-sed -i 's,SHELL=/bin/sh,SHELL=/bin/bash,' /etc/default/useradd
-
 # as the Pi does not have a hardware clock we need a fake one
 apt-get install -y \
   --no-install-recommends \

builder/test-integration/spec/hypriotos-image/base/users_spec.rb

@@ -49,9 +49,3 @@
   it { should be_mode 644 }
   it { should be_owned_by 'pirate' }
 end
-
-describe file('/etc/default/useradd') do
-  it { should be_file }
-  it { should be_owned_by 'root' }
-  its(:content) { should contain /SHELL=\/bin\/bash/ }
-end