Erase by stream ID instead of iterator.
Erase by stream ID instead of iterator.

Summary: If the onByteEventCanceled callback changes the map then the iterator will no longer be valid.

Reviewed By: lnicco

Differential Revision: D25283060

fbshipit-source-id: e32bc8bc343d8d50785985a0bb607ab43188e464

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst