[isolate] Fix delete () call to operator delete form.

This is follow-up to 9e636b5.

Change-Id: Ia167e9faea9b3085fdc1076666d05360646153e9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/121942
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>

Author: aam

runtime/vm/isolate.cc

@@ -417,7 +417,7 @@ void IsolateGroup::Cleanup() {
   delete isolate_groups_rwlock_;
   isolate_groups_rwlock_ = nullptr;
   ASSERT(isolate_groups_->IsEmpty());
-  delete (isolate_groups_);
+  delete isolate_groups_;
   isolate_groups_ = nullptr;
 }