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.
This is a requirement for roccat-tools, which is going to be introduced
soon.
The reason why I'm using propagatedBuildInputs here is because the
pkg-config file lists *all* of the dependencies in Requires and
Requires.private, so those libraries are needed whenever any software
uses that library.
Signed-off-by: aszlig <aszlig@nix.build>
