arc,hexagon: Delete asm/barrier.h

arc,hexagon: Delete asm/barrier.h

Both already use asm-generic/barrier.h as per their
include/asm/Kbuild. Remove the stale files.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-c7vlkshl3tblim0o8z2p70kt@git.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: linux-hexagon@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>