remove string value for app_name as that will now get generated in gradle

Author: JulianKast

android/hello_sdl_android/src/main/res/values/strings.xml

@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-    <string name="app_name">Hello Sdl Android</string>
     <string name="hello_world">Hello SDL!</string>
     <string name="action_settings">Settings</string>