How do you go about uninstalling TH2 and the older 'linear' processors?

There is no process for uninstalling individual plug-ins. If you do not want to see the plug-ins. the most expedient solution is using the exclude option in the plug-in manager.

Elffin
How do you go about uninstalling TH2 and the older 'linear' processors?

If you really want to remove them you could go to your vst folder on the Hard Drive and find the .dll files associated with these plugins.  Deleting them will get rid of them.  Though, I'll take no responsibility to what will happen.
 
I've done this with other plug ins without issue, and can only assume the same will work for these. 
 
I'd go with schook's suggestion.  

Thinking about this a little more, with the way SONAR handles TH2 to TH3 migration, it may be a good idea to delete or move the TH2 dll out of the VST scan path rather than exclude it. I am not sure excluding a plug-is enough to trigger the new "VST Persist Compatibility" feature.

I wonder if I can zip the dll  to make sure that scanner doesn't see the plugin...
 
 

Yes, the scanner skips zip files.