Remove Chromium builders from build.webkit.org
https://bugs.webkit.org/show_bug.cgi?id=113990

Reviewed by Benjamin Poulain.

Land the part to disable triggering of Chromium builders first so that we may start
deleting more Chromium code that breaks the update step.

* BuildSlaveSupport/build.webkit.org-config/config.json:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147707 268f45cc-cd09-0410-ab3c-d52691b4dbfc