Remove remains of the "new" indexer

See: https://bugs.eclipse.org/bugs/show_bug.cgi?id=579203

>There is still many code comments in jdt.core which refers to the "new index" which was removed.
example:
>```
> /**
> * The new indexer is disabled, see [bug 544898](https://bugs.eclipse.org/bugs/show_bug.cgi?id=544898)
> */
>// private Indexer indexer = Indexer.getInstance();
>```
>further hits can be found with full text search for "new index", "new Indexer", "544898"

Start with a full-text search across jdt.core for "new index", "new Indexer", and "544898", then review each matching comment or disabled code reference in context. Done means the obsolete remains of the removed "new" indexer are removed without affecting current indexing behavior; the issue does not name a specific test to run.

Written by the indexing model from the issue text.