The only shortcut here is a good memory if it's used already or not.
Honestly though, I wouldn't really worry about a few vars hanging around - unless you've literally got hundreds/thousands of unused vars, it won't make a grain of sands difference to performance or project size. If it's more of just a case of being tidy for the sake of sanity - then yeah, have fun cross checking everything :/
Yeah, it's basically just my OCD kicking in. Haha, I'm not worried about filesize or performance. But it just get a bit hard working after a while because i named them very similar in many cases. posX, Xpos, Xsort, Xvar, objectX, Xtest, testX and all other combinations you can think of. The biggest problem is remembering which was the actual one I was using. Lol.
So a nice little C2 cleanup functionality would be great. Things like "Delete unused instance variables, delete unused sprires" and things like that.