Remove custom gdk base image

What does this MR do and why?

Change in gitlab project have been introduced to not rely on custom gdk base image and use the one built in gdk project itself. This removes the job that was building said image.

Checklist

• (If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.