Collection matchers removals

So this stops loading the collection matchers gem.  Is there anything else to do, @JonRowe?  I noticed there's still ActiveModel/ActiveRecord extensions that provide `records` and `errors_on` methods that work with the `have` matchers...we may want to move those into the `rspec-collection_matchers` gem, although they are kinda useful as APIs in their own right.  Then again, we're monkey patching rails and that's probably a bad idea.

I'm not really sure what you had planned here but figured I'd open this to get this going.

(BTW, I built this on top of #1002 so it's targetting that branch for now so you can see the diff).