6.1 SP4:

msiexec.exe /quiet /X {70E2321C-0B8E-4F4D-A5DD-8D3180C67867}

6.1 SP6:

msiexec.exe /quiet /X {1903A336-191A-4798-BA16-C77BF7CDA89E}

Admin privileges required.

Note that the system will reboot automatically after completing the uninstall, so you may want to change the parameters to msiexec to include /norestart or /promptrestart, though you will have to make sure that the system is rebooted before attempting to install any version again.  You could allow the user to interact with the uninstall by removing the /quiet, but then they have the opportunity to cancel the uninstall.

Since the product code changes every release, if you want a solution for any version, you will need to create a script to enumerate the HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall key and look for a subkey with a value "DisplayName" set to "Symantec Workspace Virtualization Agent" and then that subkey name is the product code to pass to msiexec.exe.  This is left as an exercise for the reader.