Don't show full backtrace for rspec failures

This was making me sad, because I had to scroll past all the lines that implement the rspec example groups and matchers... none of which is at all interesting.

@jrafanie added the option so we don't miss out on lines from our customized rails.

So instead, I'll just remove any filter that would affect `ActiveRecord::Base.connection`, as a simple proxy for "any of rails".
(done)