Summary
-------

Remove the antiquated `jhat` tool.


Motivation
----------

`jhat` was added in JDK 6, based upon the java.net [HAT project][hat].
`jhat` is an experimental, unsupported, and out-of-date tool.  Superior
heap visualizers and analyzers have now been available for many years.

[hat]: https://java.net/projects/hat


Description
-----------

Stop building and shipping the `jhat` tool in the JDK.

Document this change in the appropriate release notes.  Very few people
are using this tool, so the impact on users should be minimal.  The tool
has long been marked for removal in the documentation with the words:

> NOTE: This tool is experimental and may not be available in future
  versions of the JDK.


Testing
-------

Existing `jhat` tests will need to be removed.

Some existing tests for `hprof` file creation use `jhat` to validate the
files.  We'll need to preserve the `jhat` `hprof` file parser/validator
for use in these tests.  That does not mean, however, that the code has
to be in the product, rather it should be part of the tests.