LOL. no, you shouldn't delete it. You have already done the "crime", as it were. If you are caught, it doesn't matter if you deleted it. Might as well just hold on to it, enjoy the music, and support the bands by going to their shows or buying their music in the future if that helps your conscience feel any better about itself.
And yes, the only thing keeping you from using that upgrade on both is your moral compass. In other words, it's up to you. I must say that I really like the "trust begets trust" idea that Apple has regarding licensing for most of their software... In fact, OSX is about the only OS/software I willingly pay for, and I think it has something to do with how nice they are about the licenses (that and it is actually high quality software that I use every single day)...