Remove unused events.

service/UI/UIEvents.js

-var UIEvents = {
-    NICKNAME_CHANGED: "UI.nickname_changed",
-    SELECTED_ENDPOINT: "UI.selected_endpoint",
-    PINNED_ENDPOINT: "UI.pinned_endpoint",
-    LARGEVIDEO_INIT: "UI.largevideo_init"
-};
-module.exports = UIEvents;