javac provides the ability to use a custom private implementation of code to read zip files. As we transition towards using NIO file systems within javac, we should remove this private internal library.

The classes to be removed are:
    javac.file.ZipFileIndex
    javac.file.ZipFileIndexArchive
    javac.file.ZipFileIndexCache

In addition, JavacFileManager will be simplified to not support these classes. The feature was controlled by undocumented -XD options, so no CCC will be required to remove this support.