libfetch: remove all old OpenSSL support

This change removes pre-OpenSSL 1.1 supporting code and removes/adjusted
preprocessor conditionals which were tautilogically true as FreeBSD main
has shipped with OpenSSL 1.1+ for some time.

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D40711

(cherry picked from commit bc1027a7785166fde9c2a3b48e6e70d198377d4b)