Plt-4483 Removed unnecessary events from ChannelStore (#4407)

* PLT-4483 Removed MoreChange listener from ChannelStore

* PLT-4483 Removed LeaveChannel listener from ChannelStore

webapp/utils/constants.jsx

@@ -63,7 +63,6 @@ export const ActionTypes = keyMirror({
 
     CLICK_CHANNEL: null,
     CREATE_CHANNEL: null,
-    LEAVE_CHANNEL: null,
     CREATE_POST: null,
     CREATE_COMMENT: null,
     POST_DELETED: null,