chore(): cleanup return values

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

src/plugins/datepicker.ts

@@ -99,13 +99,6 @@ export class DatePicker {
    * @returns {Promise<Date>} Returns a promise that resolves with the picked date and/or time, or rejects with an error.
    */
   @Cordova()
-  static show(options: datePickerOptions): Promise<Date> {
-    // 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<Date>((res, rej) => {});
-  }
+  static show(options: datePickerOptions): Promise<Date> { return }
 
 }