Cancel calls to rate-limited funcs on unmount

The tests were throwing up warnings about state being accessed, and null
MatrixClients being called, after component unmount.

src/components/views/rooms/MemberList.js

@@ -81,6 +81,9 @@ module.exports = React.createClass({
             cli.removeListener("User.lastPresenceTs", this.onUserLastPresenceTs);
             // cli.removeListener("Room.timeline", this.onRoomTimeline);
         }
+
+        // cancel any pending calls to the rate_limited_funcs
+        this._updateList.cancelPendingCall();
     },
 
 /*