libfs: kill empty_dir_getattr()

libfs: kill empty_dir_getattr()

It's used only to initialize ->getattr in one inode_operations instance
(empty_dir_inode_operations) and its behaviour had always been equivalent
to what we get with NULL ->getattr.

Just remove that initializer, along with empty_dir_getattr() itself.
While we are at it, the same instance has ->permission initialized to
generic_permission, which is what NULL ->permission ends up doing.
Again, no point keeping it.

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