libkeynote: use DSA_generate_parameters_ex()

libkeynote: use DSA_generate_parameters_ex()

DSA_generate_parameters() was deprecated in 2002. Its removal was blocked
because someone added "enhanced DSA support" to rust-openssl. Fortunately
this was fixed recently by the pyca people. So we can remove it now.

Of course, DSA_generate_parameters_ex() wasn't an improvement. While it no
longer uses the old callback version, it also needs a DSA object passed in
thus making it more annoying for callers.

ok jsing