checkpatch: Remove checks relating to [smp_]read_barrier_depends()

The [smp_]read_barrier_depends() macros no longer exist, so we don't
need to deal with them in the checkpatch script.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>