ceph: remove a few bogus declarations

There are three ceph page vector functions declared in
"fs/ceph/super.h" that don't belong there.  They're
probably left over from some long-ago code reorganization.

They're properly declared in "include/linux/ceph/libceph.h"
so just delete the ones in "super.h".

This and the next few commits resolve:
    http://tracker.ceph.com/issues/4053



Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>