Revert "use fullname where this can be extracted: add google format version (#6)"

[sbernauer]

This reverts commit e6d2d60.

Description

Reverting the change, as this introduced the following security risk:

Imagine the situation the user hbase/hbase-prod.prod-namespace.svc.cluster.local@CLUSTER.LOCAL access HDFS, the GroupMapper will be asked for the groups of the user hbase and returns the groups ["prod"]. This response will be cached by HDFS by the key hbase. If a different user hbase/hbase-dev.dev-namespace.svc.cluster.local@CLUSTER.LOCAL accesses HDFS a few seconds later the mapping hbase -> ["prod"] is still cached and HDFS will falsely assume the hbase-dev HBase is in the prod group!

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# Reviewer
- [ ] Code contains useful comments
- [ ] (Integration-)Test cases added
- [ ] Documentation added or updated
- [ ] Changelog updated

# Acceptance
- [ ] Proper release label has been added