A lot of bloat had been accumulated through updates (e.g. with linphone
migrating from Gtk to Qt, or linphone being split to liblinphone &
linphone-desktop).
Method: Through trial and error. Delete all dependencies, try to build, try to
run, reintroduce missing dependencies.
I have tested everything I could, but it is possible that some optional
features have been silently disabled with dependencies not being found now.
(Codecs, encryption schemes, etc...)
continuation of #109595
pkgconfig was aliased in 2018, however, it remained in
all-packages.nix due to its wide usage. This cleans
up the remaining references to pkgs.pkgsconfig and
moves the entry to aliases.nix.
python3Packages.pkgconfig remained unchanged because
it's the canonical name of the upstream package
on pypi.
After making `ffmpeg` point to the latest `ffmpeg_4`, all packages that
used `ffmpeg` without requiring a specific version now use ffmpeg_3
explicitly so they shouldn't change.
