Since b2f9cd34e7 ("gobject-introspection: use wrapper.nix for the
native package too so we can propagate the dev output"),
gobject-introspection doesn't need to be included in buildInputs when
it's in nativeBuildInputs, as it's propagated from the setup hook.
Removing the build input fixes evaluation in buildPackages when
cross-compiling to platforms that gobject-introspection is unsupported
on, like ghcjs.
Tested building natively on x86_64-linux, in
pkgsCross.aarch64-multiplatform, and in pkgsCross.ghcjs.buildPackages.
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.
