Pass connection rather than alias_tracker

Because we're only using the `connection` so passing the entire tracker isn't unnecessary.

Eventually only the `connection` will be passed to `add_constraints` with later refactoring but currently that's not possible because of `construct_tables` method.

@tenderlove - when we worked on this on the `add_constraints` refactoring branch I don't think we realized we couldn't pull tracker out of `add_constraints` on master because our branch doesn't have `construct_tables` anymore. I think this is the best solution until that refactoring on `add_constraints` is ready to be merged :grin: