x86, um: uml atomic.h is not needed anymore

Its only difference from underlying atomic.h used to be the include
of kernel.h; it's not needed there anymore.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/um/include/asm/atomic.h

-#ifndef __UM_ATOMIC_H
-#define __UM_ATOMIC_H
-
-/* The i386 atomic.h calls printk, but doesn't include kernel.h, so we
- * include it here.
- */
-#include "linux/kernel.h"
-
-#include "asm/arch/atomic.h"
-
-#endif