x86-64: eliminate dead code

Signed-off-by: NJan Beulich <jbeulich@novell.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/asm-x86/mmu.h

@@ -7,14 +7,9 @@
 /*
  * The x86 doesn't have a mmu context, but
  * we put the segment information here.
- *
- * cpu_vm_mask is used to optimize ldt flushing.
  */
 typedef struct {
 	void *ldt;
-#ifdef CONFIG_X86_64
-	rwlock_t ldtlock;
-#endif
 	int size;
 	struct mutex lock;
 	void *vdso;