locking: Remove deprecated smp_mb__() barriers

Its been a while and there are no in-tree users left, so remove the
deprecated barriers.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Chen, Gong <gong.chen@linux.intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Joe Perches <joe@perches.com>
Cc: John Sullivan <jsrhbz@kanargh.force9.co.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>