Register shortcuts on window instead of globally

Summary:
Changelog: Register shortcuts only for Flipper application instead of globally. Fixes https://github.com/facebook/flipper/issues/3090

As reported, during decapitation we accidentally started registering shortcuts globally, rather per app as it used to be in the menu's. This diff fixes that and also makes sure shortcuts are supported in the browser version of flipper

Reviewed By: lawrencelomax

Differential Revision: D33158445

fbshipit-source-id: 8371e5b96e772152eeb93ba990e1f5edb9e67085

desktop/flipper-ui-browser/src/initializeRenderHost.tsx

@@ -31,10 +31,6 @@ export function initializeRenderHost(
     openLink(url: string) {
       window.open(url, '_blank');
     },
-    registerShortcut(_shortcut, _callback) {
-      // TODO:
-      return () => {};
-    },
     hasFocus() {
       return document.hasFocus();
     },