Remove GCM installation - it's no longer needed

The push-plugin now depends on the nativescript-plugin-google-play-services, so the addition of the GCM library is no longer needed.

Author: yyosifov

README.md

@@ -26,11 +26,6 @@ The code for the Push Plugin for NativeScript.
 
 		tns platform add android
 
-- Add Google Play Services, as GCM is part of it. It's present in the android-sdk. Add it like this (NOTE: your path may be different, it depends on the installation path of the Android SDK):
-
-		tns library add android C:\Users\your_user_name\AppData\Local\Android\android-sdk\extras\google\google_play_services\libproject\google-play-services_lib\libs
-
-
 - Add sample code in app/main-view-model.js in the function HelloWorldModel() like this one to subscribe and receive messages (Enter your google project number in the options of the register method):
 
 ```javascript