How to remove HTC Sync calendar entries?
These are the steps I took on my HTC Desire running Android version 2.2 to delete all calendar data, and in turn the PC Sync calendar:


On the phone, open Settings > Applications > Manage Applications
Click the “All” tab at the top of the screen
Scroll down and tap the Calendar Storage application
Tap the “Clear data” button, and confirm you’d like to proceed.


Now all the calendar data is gone from the phone, running your sync processes again to populate only the calendars you want on your phone.