futex: Cleanup stale fshared flag interfaces

The fast GUP changes stopped using the fshared flag in
put_futex_keys(), but we kept the interface the same.

Cleanup all stale users.

This patch is split out from Darren Harts combo patch which also
combines various flags. This way the changes are clearly separated.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Darren Hart <dvhart@linux.intel.com>
LKML-Reference: <1289250609-16304-1-git-send-email-dvhart@linux.intel.com>