Removing code that we shouldn't need now that 3.6 is EOL

Minimal testing shows that this works, but it wants more poking before I
ship it as a tagged version.  I've tested on a dist with DB steps, we
want to test on several other dists first.
Explicitly require RT::Handle

If you're not make database changes, you need to require RT::Handle
explicitly
Merge branch 'remove-cmp_versions'