ssl: move CertificateRequest to ssl-utils

Except for field/expert_info names, a redundant subtree assignment,
a different !tree check, a type confusion in DTLS (proto_tree *ti),
a check against a different DTLS/TLS version and a (void) retval cast,
the functions are exactly the same. Extract them to ssl-utils.

Change-Id: I2ca7089fe2cd23212ef78656506cb53768f55927
Reviewed-on: https://code.wireshark.org/review/2986
Reviewed-by: Anders Broman <a.broman58@gmail.com>