Summary: [Reported in the support request](https://fb.workplace.com/groups/flippersupport/posts/1237466586733997/), Activity object is held by ObjectTracker even though the Activity is destroyed. This, in this case, caused strict mode in Portal app to forcibly terminate. This diff tried to remove activities from the reference holder. Reviewed By: passy Differential Revision: D31828290 fbshipit-source-id: aad7e8d7ba14069f8dd7c654a3604d482d85e110