simple_recursive_removal(): saner interaction with fsnotify

Make it match the real unlink(2)/rmdir(2) - notify *after* the
operation.  And use fsnotify_delete() instead of messing with
fsnotify_unlink()/fsnotify_rmdir().

Currently the only caller that cares is the one in debugfs, and
there the order matching the normal syscalls makes more sense;
it'll get more serious for users introduced later in the series.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>