chore(): remove returned Promises

Addresses: https://github.com/driftyco/ionic-native/issues/38.

src/plugins/appavailability.ts

@@ -38,13 +38,6 @@ export class AppAvailability {
    * @returns {Promise<boolean>}
    */
   @Cordova()
-  static check(app : string) : Promise<any> {
-    // This Promise is replaced by one from the @Cordova decorator that wraps
-    // the plugin's callbacks. We provide a dummy one here so TypeScript
-    // knows that the correct return type is Promise, because there's no way
-    // for it to know the return type from a decorator.
-    // See https://github.com/Microsoft/TypeScript/issues/4881
-    return new Promise<boolean>((res, rej) => {});
-  }
+  static check(app: string): Promise<boolean> { return }
 
 }