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.
The removes the "-internal" suffix from the OpenJDK version string.
Some applications, like the Jetbrains IDEs, check for a suffix to
determine if a stable JDK is used.
Thanks to @liff for the hint in #92837!
