Zorg migration to GitHub/monorepo - Done

Hello everyone,

Zorg migration to GitHub/monorepo is complete.

I have removed the following builders from the production build bot:

* clang-atom-d525-fedora-rel - fails to checkout from github
* clang-x64-ninja-win7 - fails to checkout from github
* polly-amd64-linux - missing git
* llvm-hexagon-elf - does not support github

The rest of the builders are working well. The whole production build
bot is back to normal.

Thank you for your patience and understanding.
Please let me know if you see any issue with the build bot.