KVM: x86 emulator: merge the two emulate_1op_rax_rdx implementations

We have two emulate-with-extended-accumulator implementations: once
which expect traps (_ex) and one which doesn't (plain).  Drop the
plain implementation and always use the one which expects traps;
it will simply return 0 in the _ex argument and we can happily ignore
it.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>