Because I just tried it, does not seem to work for me. Command that I tried:
rclone link gdrive:foo.zip --unlink
P.S: I need to unshare 200k files in a directory. How do I do that?
I think you are right, it isn't supported for google drive.
It doesn't look too hard to implement if you wanted to have a go?
Only if I could. 
There are some ideas in this thread you might find helpful