Delete all instances of asm/system.h

Delete all instances of asm/system.h as they should be redundant by this
point.

Signed-off-by: David Howells <dhowells@redhat.com>

arch/openrisc/include/asm/system.h

@@ -1,5 +0,0 @@
-/* FILE TO BE DELETED. DO NOT ADD STUFF HERE! */
-#include <asm/barrier.h>
-#include <asm/cmpxchg.h>
-#include <asm/exec.h>
-#include <asm/switch_to.h>