Remove unused variable in imemo.c

The variable klass is only used in debug builds and generates a warning
on non-debug builds.

imemo.c

@@ -182,7 +182,6 @@ static enum rb_id_table_iterator_result
 cc_table_mark_i(ID id, VALUE ccs_ptr, void *data)
 {
     struct rb_class_cc_entries *ccs = (struct rb_class_cc_entries *)ccs_ptr;
-    VALUE klass = (VALUE)data;
     VM_ASSERT(vm_ccs_p(ccs));
     VM_ASSERT(id == ccs->cme->called_id);
 
@@ -194,7 +193,7 @@ cc_table_mark_i(ID id, VALUE ccs_ptr, void *data)
         rb_gc_mark_movable((VALUE)ccs->cme);
 
         for (int i=0; i<ccs->len; i++) {
-            VM_ASSERT(klass == ccs->entries[i].cc->klass);
+            VM_ASSERT((VALUE)data == ccs->entries[i].cc->klass);
             VM_ASSERT(vm_cc_check_cme(ccs->entries[i].cc, ccs->cme));
 
             rb_gc_mark_movable((VALUE)ccs->entries[i].ci);