Consider removing LUCENE JIRA versions 5.x and 6.x and fixing issues to refer to the correct version [LUCENE-7275]

The LUCENE JIRA project (but not the SOLR one) has versions `6.x` and `5.x` - there are 38 issues with these as fixVersion-s: .

Should we even have `6.x` and `5.x` versions at all?

If we get rid of them, all affected issues (which may be a larger number than those retrieved with the above query, since these versions could also have been used in JIRA's "Affects Version/s" field) will need to be relabeled with the appropriate version.

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Migrated from [LUCENE-7275](https://issues.apache.org/jira/browse/LUCENE-7275) by Steven Rowe (@sarowe)
Linked issues:
- #8326

Start with the linked JIRA query and inspect every issue using 5.x or 6.x in Fix Version/s or Affects Version/s. Decide the appropriate replacement version for each affected issue, then remove the obsolete versions and verify that no incorrect references remain.

Written by the indexing model from the issue text.