SLES: remove tags for dedicated runner, use shared runner with new container

Remove the tags for the SLES builds, so that the shared runners will be used when on dev.

Related to #2254 (closed)

I was looking at the possibility of also removing the different script/only/etc for the SLES jobs, but I am unsure as to why they are different from the rest of the jobs. There are a few steps that don't line up identically, and this is why I have this as a WIP at the moment

• Templated &tag_build: https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/.gitlab-ci.yml#L193
• SLES tag build: https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/.gitlab-ci.yml#L650