docs/about/deprecated: Mark HAXM in QEMU as deprecated

docs/about/deprecated: Mark HAXM in QEMU as deprecated

The HAXM project has been retired (see https://github.com/intel/haxm#status),
so we should mark the code in QEMU as deprecated (and finally remove it
unless somebody else picks the project up again - which is quite unlikely
since there are now whpx and hvf on these operating systems, too).

Message-Id: <20230126121034.1035138-1-thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>