There are still some, but those are in actual code that's used outside core, so the change there would need to go through the deprecation cycle. That's a task for another day.
It's very easy to forget to add `require 'rails_helper'` at the top of every core/plugin spec file, and omissions can cause some very confusing/sporadic errors.
By setting this flag in `.rspec`, we can remove the need for `require 'rails_helper'` entirely.
