Use the newer names for STACK_OF(T) functions with BoringSSL

This is yet another symptom of
https://github.com/sfackler/rust-openssl/issues/1944.

Ideally rust-openssl would use the type-safe wrappers, which are the
actual public APIs. Right now, rust-openssl's STACK_OF(T) handling is a
safety regression from C. This PR doesn't address the safety issue, only
works around the BoringSSL porting issue.