Cleanup cruft in double spec.

While investigating double_spec, I spent a few minutes trying to understand the call to `violated`, before I realized it was probably there to ensure an exception was raised if the expectation code failed. While `raise_error` potentially failing is a valid concern, it doesn't seem like something that should be verified in this spec.

A few specs, the line number ones, were still relying on this behavior to verify correctness, so I changed those to use a more modern style of rspec.

I tracked the inclusion of the `violated` calls to this commit, which leads me to believe they've been there a while and can be safely removed. :) https://github.com/rspec/rspec-mocks/blob/a64df194cccf5acb9dbdc0b18154d7a1ceebfc37/spec/spec/mocks/mock_spec.rb