Remove Cobertura from our build process
We're having trouble with Cobertura, and we noticed that we're not really using it that much: One issue is an UnsupportedClassVersionError (#31233 (moved)), another issue is a CI fail due to line coverage rate of 91.6% being below 92.0% on the CI host which doesn't show on my dev machine.
Without having hard evidence, I suspect that these issues are in one way or another related to Cobertura not being maintained anymore with its last release being from February 2015.
Let's remove Cobertura from our build process. We can later switch to using something else that GitLab can actually interpret the output of.
I didn't work on these changes yet, but I think this mainly requires changes to metrics-base and a subsequent update in all depending code bases. I'll work on this later today or tomorrow.