accel: Remove HAX accelerator

HAX is deprecated since commits 73741fda ("MAINTAINERS: Abort
HAXM maintenance") and 90c167a1 ("docs/about/deprecated: Mark
HAXM in QEMU as deprecated"), released in v8.0.0.

Per the latest HAXM release (v7.8 [*]), the latest QEMU supported
is v7.2:

  Note: Up to this release, HAXM supports QEMU from 2.9.0 to 7.2.0.

The next commit (https://github.com/intel/haxm/commit/da1b8ec072)
added:

  HAXM v7.8.0 is our last release and we will not accept
  pull requests or respond to issues after this.

It became very hard to build and test HAXM. Its previous
maintainers made it clear they won't help.  It doesn't seem to be
a very good use of QEMU maintainers to spend their time in a dead
project. Save our time by removing this orphan zombie code.

[*] https://github.com/intel/haxm/releases/tag/v7.8.0



Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230831082016.60885-1-philmd@linaro.org>