Cleanup CI scripts (#12205)

* Delete unused scripts

- gen_tags.sh: not the right file, produce garbage even if path is fixed
- premoderator.sh: not used since ef6d24a49 (CI require a 'lgtm' or
  'ok-to-test' labels to pass (#11251), 2024-05-31)
- gitlab-branch-cleanup: unused AFAICT

* CI: inline molecule logs

Single use site -> less indirection makes it easier to read.

tests/scripts/molecule_logs.sh

@@ -1,9 +0,0 @@
-#!/bin/bash
-
-# Ensure a clean environent
-rm -fr molecule_logs
-mkdir -p molecule_logs
-
-# Collect and archive the logs
-find ~/.cache/molecule/ -name \*.out -o -name \*.err -type f | xargs tar -uf molecule_logs/molecule.tar
-gzip molecule_logs/molecule.tar