Remove superfluous include of string.h from percpu.h

There's nothing in percpu.h that requires an explicit inclusion of
string.h.
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/percpu.h

@@ -4,7 +4,6 @@
 #include <linux/preempt.h>
 #include <linux/slab.h> /* For kmalloc() */
 #include <linux/smp.h>
-#include <linux/string.h> /* For memset() */
 #include <linux/cpumask.h>
 
 #include <asm/percpu.h>