fs: remove experimental from promises.rmdir recursive

This was missed in commit 35b17d9a.

Refs: https://github.com/nodejs/node/issues/34278
Refs: https://github.com/nodejs/node/pull/35171



Signed-off-by: Anders Kaseorg <andersk@mit.edu>

PR-URL: https://github.com/nodejs/node/pull/36131


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ben Coe <bencoe@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>