Remove old Gittip files/info

There are a lot of traces to old Gittip info. Honestly, there are probably a lot of old files beyond the scope of just Gittip that could be removed.

Anyway, [this file](https://github.com/bountysource/core/blob/master/.env.dev) and [this file](https://github.com/bountysource/core/blob/master/.env.test) in particular contain old Gittip variables, which can likely be removed. I'd imagine that the `.env` file on the server does as well, but that's not something I can view/edit.

If anyone notices other old files, let me know and I'll compile it all into a PR.

Review .env.dev and .env.test first, looking for the old Gittip variables described in the issue. Check the repository for other explicitly identified Gittip traces only if their removal scope can be confirmed; done means obsolete Gittip configuration is removed without affecting current environment settings.

Written by the indexing model from the issue text.