Remove and refactor rspec-its use

[dduugg]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

its was removed from RSpec 3, but available as a separate gem for backcompat. One rationale was that it was more meta than it was in line with RSpec's documentation approach.
That gem has seen one (minor) change in the past nine years.
We only use it in a handful (11) of files, and not in a way that seems especially compact or otherwise worth the trouble (IMO).
Let's just push fully forward into RSpec 3 instead.

[MikeMcQuaid]

Looks good to me, thanks again @dduugg!