arm: Remove last_fault_code

It is unused since the removal of pmap-v4.c in commit b88b275145.

MFC after:	1 week
Sponsored by:	The FreeBSD Foundation

sys/arm/arm/trap-v6.c

@@ -70,10 +70,6 @@ __FBSDID("$FreeBSD$");
 
 extern char cachebailout[];
 
-#ifdef DEBUG
-int last_fault_code;	/* For the benefit of pmap_fault_fixup() */
-#endif
-
 struct ksig {
 	int sig;
 	u_long code;
@@ -495,10 +491,6 @@ abort_handler(struct trapframe *tf, int prefetch)
 	if (prefetch)
 		ftype |= VM_PROT_EXECUTE;
 
-#ifdef DEBUG
-	last_fault_code = fsr;
-#endif
-
 #ifdef INVARIANTS
 	onfault = pcb->pcb_onfault;
 	pcb->pcb_onfault = NULL;