Previously, I’ve installed the standalone version of Halion Sonic SE 3 because Dorico was hanging with the included VST engine (which was version 2). Now I’ve bought a Dorico 2 license and I’m a little obsessed with getting rid of stuff I don’t need on my computer because I don’t like the thought of old, unused software cluttering up my computer. So, I wanted to deregister and uninstall the standalone HSSE (and eventually Dorico 1), but somehow I can’t remove the license(s) in the eLicenser Control Center. Do I have to remove the programs first or is there another trick to it?
There’s no need to deregister licenses. And they hardly take up any space on your computer, just a few dozen bytes. If that should pose a problem to your system, then you have other, much greater problems.
I know, I also have more than enough space on my hard drive, that’s not the (primary) issue. I’d just like to have a clean and orderly system; call it an OCD, if you like. 
For example, it bothers me that HSSE always shows up in my search results when searching the system for something that contains the string “hal”. And so, if I remove HSSE I also want the license to be gone because I can’t stand stray, non-functional remainders of software on my computer.
I went through the procedure just last week.
After reinstalling just the eLicenser I had to online register the new eLicenser and reactivate the valid software. Afterwards I had a ‘clean’ eLicenser. I think it was in that order…