x86/emul: Hold x86_emulate() to strict X86EMUL_EXCEPTION requirements

x86/emul: Hold x86_emulate() to strict X86EMUL_EXCEPTION requirements

All known paths raising faults behind the back of the emulator have been
fixed.  Reinstate the original intended assertion concerning the behaviour of
X86EMUL_EXCEPTION and ctxt->event_pending.

As x86_emulate_wrapper() now covers both PV and HVM guests properly, there is
no need for the PV assertions following calls to x86_emulate().

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>