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

    nix fmt

shell.nix

@@ -19,7 +19,7 @@ let
   inherit (import ./ci { inherit nixpkgs system; }) pkgs fmt;
 
   # For `nix-shell -A hello`
-  curPkgs = builtins.removeAttrs (import ./. { inherit system; }) [
+  curPkgs = removeAttrs (import ./. { inherit system; }) [
     # Although this is what anyone may expect from a `_type = "pkgs"`,
     # this file is intended to produce a shell in the first place,
     # and a `_type` tag could confuse some code.