Alway focus on touchstart

The new gesture detection code will always prevent the default behaviour
of touchstart, so this check no longer works properly. We might want to
add something similar to GestureHandler in the future, but let's wait
and see what use cases are requested.

core/rfb.js

@@ -588,11 +588,6 @@ export default class RFB extends EventTargetMixin {
     }
 
     _focusCanvas(event) {
-        // Respect earlier handlers' request to not do side-effects
-        if (event.defaultPrevented) {
-            return;
-        }
-
         if (!this.focusOnClick) {
             return;
         }