Remove leave check

1. It's wrong because it doesn't consider the ban state
2. This should be caught by whether they have permission to send
   the event in the first place rather than worrying about whether
   it has notification permission or not

src/models/room-state.js

@@ -403,7 +403,7 @@ RoomState.prototype._maySendEventOfType = function(eventType, userId, state) {
  */
 RoomState.prototype.mayTriggerNotifOfType = function(notifLevelKey, userId) {
     const member = this.getMember(userId);
-    if (!member || member.membership == 'leave') {
+    if (!member) {
         return false;
     }