fs: Avoid userspace mounting anon_inodefs filesystem

anon_inodefs filesystem is a kernel internal filesystem userspace
shouldn't mess with. Remove registration of it so userspace cannot
even try to mount it (which would fail anyway because the filesystem is
MS_NOUSER).

This fixes an oops triggered by trinity when it tried mounting
anon_inodefs which overwrote anon_inode_inode pointer while other CPU
has been in anon_inode_getfile() between ihold() and d_instantiate().
Thus effectively creating dentry pointing to an inode without holding a
reference to it.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs: remove now stale label in anon_inode_init()

The previous commit removed the register_filesystem() call and the
associated error handling, but left the label for the error path that no
longer exists.  Remove that too.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>