Fix assertion failure when checking named-checkconf version

The dst_lib_destroy() should be called only if dst_lib_init() was called
before.  In named-checkconf, that is guarded by dst_cleanup variable
that was erroneously set to true by default.  Set the dst_cleanup to
'false' by default.

(cherry picked from commit c54880e3fa)

bin/check/named-checkconf.c

@@ -593,7 +593,7 @@ main(int argc, char **argv) {
 	const char *conffile = NULL;
 	isc_mem_t *mctx = NULL;
 	isc_result_t result = ISC_R_SUCCESS;
-	bool cleanup_dst = true;
+	bool cleanup_dst = false;
 	bool load_zones = false;
 	bool list_zones = false;
 	bool print = false;