Uninstall CodeClimate: service is defunct

[olleolleolle]

This Issue has two parts:

• Remove CodeClimate configuration from the code see Drop CodeClimate badge, configuration file #2223
• In Settings, remove the Branch requirement "codeclimate has to run" (for the branch to be considered a green build) - this requires an owner of the repo to do that

The benefit is that our work in the repo will feel clearer: when the build is green, it means it's good.

[matyikriszta]

Resolved by #2223