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.

src/ssl_crtlist.c

@@ -1530,7 +1530,7 @@ static int cli_parse_del_crtlist(char **args, char *payload, struct appctx *appc
 			LIST_DELETE(&link_ref->list);
 			free(link_ref);
 		}
-		free(inst);
+		ckch_inst_free(inst);
 	}
 
 	crtlist_free_filters(entry->filters);