[admob] Remove unused static method

lib/modules/admob/index.js

@@ -77,10 +77,6 @@ export default class Admob extends Base {
     return new RewardedVideo(this, adUnit);
   }
 
-  static get statics() {
-    return statics;
-  }
-
   get namespace(): string {
     return 'firebase:admob';
   }