Remove old-tests.

It looks like the original plan was to move tests from `old-tests` back into `tests` as we moved forward, but it looks like the `old-tests` directory hasn't been modified since the original `jj-abrams` branch landed.

I am not sure exactly why these are still around. If they serve a good purpose let's leave them in, but they are not being used in the actual QUnit test runs or ran via `ember-dev`.

If they serve no purpose, can we remove them? It makes `ack`ing and find in project searches much easier.