chore(overlay): remove deprecated ion-overlay

ionic/components/overlay/overlay.ts

@@ -1,18 +0,0 @@
-import {Directive} from 'angular2/core';
-
-/**
- * @private
- */
-@Directive({
-  selector: 'ion-overlay'
-})
-export class OverlayNav {
-
-  constructor() {
-    // deprecated warning
-    console.warn('<ion-overlay> is no longer needed and can be safely removed.');
-    console.warn('https://github.com/driftyco/ionic2/blob/master/CHANGELOG.md#overlay-refactor');
-    console.warn('See the v2 docs for an update on how overlays work.');
-  }
-
-}