MINOR: ssl/cli: 'del ssl crt-list' delete an entry

MINOR: ssl/cli: 'del ssl crt-list' delete an entry

Delete an entry in a crt-list, this is done by iterating over the
ckch_inst in the crtlist_entry. For each ckch_inst the bind_conf lock is
held during the deletion of the sni_ctx in the SNI trees. Everything
is free'd.

If there is several entries with the same certificate, a line number
must be provided to chose with entry delete.