deleteAll() does not remove all TaxonomyWriter files [LUCENE-4884]

When calling deleteAll() on the IndexWriter, the documents are removed from the index and from the taxonomy. When investigating what is happing after the deleteAll() on the disk, I see that in the index-directory I end up with just two files:

Index-directory:
- segments.gen
- segments_2

Taxonomy directory:
- segments.gen
- segments_h

BUT also a lot of 'older' files, like

- _1_Lucene41_0.tip
- _1_Lucene41_0.tim

etc.

It seems these files are never deleted. If you index a lot and call deleteAll a lot, it will fill up your disk.

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Migrated from [LUCENE-4884](https://issues.apache.org/jira/browse/LUCENE-4884) by Rob Audenaerde

Start at IndexWriter.deleteAll() and trace how deletion affects both the index-directory and taxonomy directory. Reproduce repeated deleteAll() calls while inspecting the directories, focusing on whether older taxonomy files such as _1_Lucene41_0.tip and _1_Lucene41_0.tim are removed. Done means obsolete files do not accumulate after documents and taxonomy entries are deleted.

Written by the indexing model from the issue text.