CI: Switch to plain Alpine image with modern ansible-lint

This also enables GitLab-parseable ansible-lint output.

Cf. common!26 (merged)

This also removes two unsupported and obsolete roles, as well as fixing a few (minor) issues along the way.

desktop/defaults/main.yml

 ---
 
-client_use_proprietary_google_apps: false
 client_provision_mozilla: true