Get rid of version check?

[sebastian-peter]

The version checks currently performed by Jenkins are quite restrictive, and it's not 100% clear to me how a release workflow should work here (see #753). I think we can get rid of version checks entirely because:

• with releases, I have to double check and confirm the release on sonatype anyways
• for snapshot releases, it wouldn't be the end of the world if a wrong snapshot version got published (although this could get annoying if the version was wrongly increased and dependabot would want to upgrade to the wrong version everywhere). Here, the review principle of PRs should suffice: snapshots only get deployed after a merge.