Code review comment for lp://staging/~vila/ubuntu-ci-services-itself/ts-setup

> What of this is actually needed to make your 'run-tests' work, or does it work
> as is, you just want to make these changes?

As said in the cover letter:

Drive-by fix from another branch I'm working on.

ticket_system/setup.py for the 'test' command default to injecting the list of local apps. Since that's already defined in settings.LOCAL_APPS, just use that.

Since the above was duplicating ticket_system/ticket_system/local_tests.py,
it's not needed anymore, I removed it.

I.e. the changes are unrelated, this proposal just simplify the way setup/manage restrict the tests run.