gitlab-ci: Drop tags for the jobs using Debos

While we were switching to the Debos UML backend to be able to use the autoscaling runner on AWS we introduced the aws tag to avoid the old graviera runner which was not configured to run UML.

Now the configuration for the old runner has been updated to include the tmpfs:exec on /scratch and the SYS_PTRACE capability in the Docker settings, and is thus able to run Debos with the UML backend.

We can now assume again that all the available runners configured to run untagged jobs can execute Debos just fine, so drop the tags.