x86, apic: Remove support for ia32-based Unisys ES7000

There should no longer be any ia32-based Unisys ES7000 systems out in
the wild, so remove support for it.

We've done our due diligence in reaching out to any contact information
listed for this system and no indication was given that it should be
kept around.

Signed-off-by: David Rientjes <rientjes@google.com>