I didn't use it and uninstalled it by dragging the app icon into the trash. Didn't work.
I tried the AppDelete path. No go.
I googled around and found I was not the only one. Uninstall is broken and you are basically stuck with a prompt twice a day to install the Google Music app until you reinstall your OS or go slogging through the guts of your box, throwing switches you don't understand by mixing internal uninstall tutorials (ok, to be fair, this is how you do just about everything...).
In conclusion, that app is a daily annoyance and I'd caution people against installing it.