You can actually delete items manually through the user application support folder. The path should be something like this:
Mac OS > Users > Your User > Library > Application Support > Blocs 3 > brics
Now restart Blocs if already open and that deleted bric should be gone.
As to the other point about this bric not working with the latest version of Blocs I have to say I haven’t checked it, but I had no problems with an existing project that was updated only a couple weeks ago with 3.4.2 using that bric and it is working as expected on the site.