BUG/MINOR: ssl: Clear the ckch instance when deleting a crt-list line

BUG/MINOR: ssl: Clear the ckch instance when deleting a crt-list line

When deleting a crt-list line through a "del ssl crt-list" call on the
CLI, we ended up free'ing the corresponding ckch instances without fully
clearing their contents. It left some dangling references on other
objects because the attache SSL_CTX was not deleted, as well as all the
ex_data referenced by it (OCSP responses for instance).

This patch can be backported up to branch 2.4.