Also drop $gemFlags, which is no longer used in nixpkgs.

Makes it possible to query version and pname of ruby packages,
making it to the standard level of nixpkgs

This reverts commit 54271156702fc3a3f5d156df567a2a4a274bac6b, reversing
changes made to 88ee2ac331edc3ce9f9df92aaf824592473ed868.

Remove optional builtins prefixes from prelude functions by running:

    builtins=(
      abort
      baseNameOf
      break
      derivation
      derivationStrict
      dirOf
      false
      fetchGit
      fetchMercurial
      fetchTarball
      fetchTree
      fromTOML
      import
      isNull
      map
      null
      placeholder
      removeAttrs
      scopedImport
      throw
      toString
      true
    )

    fd \
      --type file \
      . \
      pkgs \
      --exec-batch sed --in-place --regexp-extended "
        s/\<builtins\.($(
          printf '%s\n' "${builtins[@]}" |
            paste --delimiter '|' --serial -
        ))\>/\1/g
      "

    nix fmt