Remove requirements from Release Notes

The minimum version of DNN is enforced by the installer, _before_ the release notes are displayed, and all of the other requirements are DNN 7 requirements, so they, too, will need to be satisfied by the time the release notes are displayed.

I'd also suggest removing the link to the checklist, since it's mostly the same basic instructions (but more out of date), but I'll leave that decision to you.
Merge pull request #91 from bdukes/patch-1

Remove requirements from Release Notes