Remove reverse VM instruction

This was previously only used by the multiple assignment code, but
is no longer needed after the multiple assignment execution order
fix.

insns.def

@@ -592,25 +592,6 @@ swap
     /* none */
 }
 
-/* reverse stack top N order. */
-DEFINE_INSN
-reverse
-(rb_num_t n)
-(...)
-(...)
-// attr rb_snum_t sp_inc = 0;
-{
-    rb_num_t i;
-    VALUE *sp = STACK_ADDR_FROM_TOP(n);
-
-    for (i=0; i<n/2; i++) {
-	VALUE v0 = sp[i];
-	VALUE v1 = TOPN(i);
-	sp[i] = v1;
-	TOPN(i) = v0;
-    }
-}
-
 /* for stack caching. */
 DEFINE_INSN_IF(STACK_CACHING)
 reput