src: clean up uv_fs_t's in module_wrap.cc

This commit adds uv_fs_req_cleanup() calls to all uses of
uv_fs_t's in src/module_wrap.cc.

PR-URL: https://github.com/nodejs/node/pull/16722


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>