x86: remove unused macro

Mr. Grep says warn_if_not_ulong() is not used anymore anywhere
in the code. So, we remove it.
Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/asm-x86/system_64.h

@@ -73,8 +73,6 @@
 #define read_barrier_depends()	do {} while(0)
 #define set_mb(var, value) do { (void) xchg(&var, value); } while (0)
 
-#define warn_if_not_ulong(x) do { unsigned long foo; (void) (&(x) == &foo); } while (0)
-
 static inline unsigned long read_cr8(void)
 {
 	unsigned long cr8;