You can download TitaniumBackup Root for free from market and remove one.
Just don't forget to make a backup of it before you remove it.
I made a backup and removed calendargoogle.apk and kept calender.apk, and no problem since last update.
The most annoying thing is that when the caller ends the call my phone reboots. Happened 2times yesterday, and 1 time while I was talking.
And I still got random reboots, but not that many as before!