Why not just leave it alone? Your computer will not run any faster or better after deleting unused registry entries. You probably have thousands of such unused entries, but they are just what they are: unused. They don't do anything.
As for the space they take up: a few bytes. If you delete such entries, the space they have taken up is still there, still unused.
Don't become obsessed with registry "cleaning"; you may end up reinstalling Windows...
I uninstalled Adobe Reader 9.4 in Windows 7 because it was not working correctely. When I now attempt to reinstall, it will not install but rather gives the error "Application already installed." I suspect that there is some part of the program left behind in the system that tells the install program that it is already installed even though it is not. I cannot open any pdf file until this is resolved. Do you have an anwer for this?