The auto-updater tool that continues downloading new versions of GTM lives in this folder:
~/Library/Application Support/CitrixOnline
Delete that folder (and empty the Trash). That should stop more copies of the GTM application from being installed.
To more thoroughly purge your system of all GTM-related files, you will need to delete the following browser plug-in...
~/Library/Internet Plug-Ins/CitrixOnlineWebDeploymentPlugin.plugin
...as well as all files or folders with names that begin "com.citrixonline." found within the following folders:
/Library/Preferences
⟵(note that this is the
global Library folder)
~/Library/Caches
~/Library/Log
~/Library/Preferences
~/Library/Preferences/ByHost
~/Library/Saved Application State
Again, be sure to empty the Trash when you're done. If the system won't allow you to completely empty the Trash because an item is in use, restart your computer and then empty the Trash again; then it should empty completely.