How do I completely remove Symantec Endpoint Protection?
Looks like there's a tool that will completely uninstall Symantec software from your Mac. This page describes how it works. Here's the direct download link to RemoveSymantecMacFiles.zip.

In case the first link goes away, the easiest way to run it is to control-click on the download, choose "Open with..." -> "Terminal" and follow the instructions. You'll need to have admin privileges on the Mac but you won't need the "Symantec Endpoint Protection Manager administrator" password.