If things work with 5.8.5 (and I don't know of any regressions that might affect you), it should be safe to delete the 5.6.1 folders. It won't hurt to keep them around, but if you're careful, it shouldn't hurt to delete them.

If you're really paranoid, you might rename them and leave them be for a while to see if all of your required applications still work. When you've satisfied your paranoia, then delete them.

Perl 5.8.x won't use those libraries by default, though, and it won't use some of them well at all.