remove or fix IndexWriter.tryDeleteDocument [LUCENE-6384]

This method is causing bugs in tests, I think its a trap.

I don't think people understand the semantics of it, and i don't like that its difficult for it to return false in tests

So its unlikely to return false in tests, only in production. Broken just like java 7 string hashing.

I think we should either remove it, rename it, fix the javadocs let IndexWriter create a random and intentionally return false from this method say 1% of the time to make it less trappy, something.

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Migrated from [LUCENE-6384](https://issues.apache.org/jira/browse/LUCENE-6384) by Robert Muir (@rmuir)

Start at IndexWriter.tryDeleteDocument and inspect its callers and the tests that exercise it. Compare the documented and observed return semantics, especially the difficulty of producing false in tests. Done requires a decided direction—removal, renaming, corrected documentation, or deliberate test coverage—and corresponding validation.

Written by the indexing model from the issue text.