NEXUS-6139: Evict unused items deletes permanently.

Seemingly we have duplicated walker processors used by
Maven proxies and everything else. The latter was
already fixed by this PR below:
https://github.com/sonatype/nexus-oss/pull/262

But as Rich detected, the fix was not applied to
Maven repositories.

Issue
https://issues.sonatype.org/browse/NEXUS-6139

CI
https://bamboo.zion.sonatype.com/browse/NX-OSSF39