Remove unneeded Android Permissions

INTERNET and WRITE_EXTERNAL_STORAGE were part of the old Xamarin.Android project templates for VS. While INTERNET is likely needed by many apps that use ServiceStack, it's confusing when it's automatically added via a third-party library. WRITE_EXTERNAL_STORAGE is not needed at all.

See http://forums.xamarin.com/discussion/16197/stuck-manifest-permissions, https://bugzilla.xamarin.com/show_bug.cgi?id=19785