ANON_INODES shouldn't be user visible

There doesn't seem to be a good reason for ANON_INODES being
an user visible option.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>