Simplify Bitrise repo slug lookup

[rogerluan]

Hey 👋

I realized that we had this issue related to Bitrise #1047 and thought it was easy enough to fix. This PR removes GIT_REPOSITORY_URL and uses other env vars that are more user friendly to parse, removing the regex completely - which's also safer and now works for all sorts of URLs.

With my little understanding of how Danger and CI interacts, I hope that simply and blindly dropping the support to GIT_REPOSITORY_URL won't break existing users' setups 😬

Resolves #1047
Docs: https://devcenter.bitrise.io/builds/available-environment-variables/

[orta]

I'm not wild on this, because I'm not certain on whether this breaks older installs -

/cc @BanyikAnna - I think bitrise is a pure PAAS, but you do you have enterprise installs etc, or does everyone have the same "version" of bitrise and thus everyone gets the same env vars on builds?

[rogerluan]

This might certainly break users who manually override the designed env vars (in this case, GIT_REPOSITORY_URL), but users shouldn't be doing that in the first place I think, so I think it's safe? Both GIT_REPOSITORY_URL and the env vars I used are global bitrise env vars so they should be the same for everyone, independent of version - unlike step-specific env vars that can be modified depending on the version of the step you're using.

I'm not sure about Bitrise Enterprise plans though, they might have a different setup. Thanks for tagging someone with knowledge on this @orta ! 🤗

[orta]

I'll give them a few days to respond, if we get nothing by next week I'll take it and treat it as a server minor

[rogerluan]

Sounds perfect! Thank you @orta 💪

[orta]

OK, let's do it