Cut binary releases down to a single format [LUCENE-6258]

In #7309, one idea discussed to decrease the size of release artifacts was removing either tgz or zip from our binary releases.

The source releases are already only in tgz. I think we should do the same for binary releases. I looked at a number of other Apache projects, and the results are mixed, but there definitely are many major projects (hadoop, couchdb, cassandra, cordova) that only release tgz. Anyone who can deal with running using Lucene or Solr should have the skills necessary to extract an archive in either format, so in this way I think either format is fine, but I think matching what we release source in has a nice look.

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Migrated from [LUCENE-6258](https://issues.apache.org/jira/browse/LUCENE-6258) by Ryan Ernst (@rjernst)

Start by reviewing Lucene's binary release packaging entry points and the discussion in issue #7309, since no specific file or test is named here. The work is complete when binary releases use one archive format, matching the chosen format consistently with source releases, and the resulting artifacts remain usable.

Written by the indexing model from the issue text.