I updated to Google Play Services 6.5 and I want to revert back to actual official version
If you open Settings > Apps > find Google Play Services and select uninstall updates, that should revert to your previous version of GPS.

I think you did the same as me, as it wasn't clear on any site that this APK wasn't suitable for the Nexus 9 - were you getting an error message with regards to GP Music as well?

AC