lib: remove optional builtins prefixes from prelude functions

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

    nix fmt

lib/types.nix

@@ -1373,7 +1373,7 @@ let
             if builtins.isString v then
               ''"${v}"''
             else if builtins.isInt v then
-              builtins.toString v
+              toString v
             else if builtins.isBool v then
               boolToString v
             else