[build.webkit.org] Delete builddir key from config.json

https://bugs.webkit.org/show_bug.cgi?id=239718

Reviewed by Jonathan Bedard.

* Tools/CISupport/build-webkit-org/config.json:

Canonical link: https://commits.webkit.org/249948@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@293325 268f45cc-cd09-0410-ab3c-d52691b4dbfc