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/structures/RoomView.js

@@ -273,6 +273,9 @@ module.exports = React.createClass({
 
         window.removeEventListener('resize', this.onResize);
 
+        // cancel any pending calls to the rate_limited_funcs
+        this._updateRoomMembers.cancelPendingCall();
+
         // no need to do this as Dir & Settings are now overlays. It just burnt CPU.
         // console.log("Tinter.tint from RoomView.unmount");
         // Tinter.tint(); // reset colourscheme