Condition code not set after CAS on aarch64

[Roland Westrelin]

> The condition code gets set in
> MacroAssembler::cmpxchg_oop_shenandoah() already. Setting it
> afterwards using cset might actually be harmful because I am not sure
> that the condition flags are correct.

I missed that indeed.

> I'd revert the whole changeset:
> http://cr.openjdk.java.net/~roland/shenandoah/aarch64-cas-cc/webrev.00/
> 
> Ok to revert?

Yes.

Roland.