Remove ECDSA_{do_,}sign_ex()

Remove ECDSA_{do_,}sign_ex()

There is no reason to keep these. It is cleaner to keep ECDSA_sign_setup()
but remove the logic for passed-in kinv and r.

Refuse to cooperate as far as possible. Someone could still implement
their own versions of ECDSA_{do_,}_sign_ex() and ECDSA_sign_setup() by
leveraging EC_KEY_METHOD_get_sign() and building their own wrappers.
We can't make such an implementation of ECDSA_sign_setup() fail, but we
make the actual signing fail since we no longer "do the right thing".

ok jsing