Refactor the dns_name API to use ISC_THREAD_LOCAL

Previously, the dns_name API used isc_thread_key API for TLS, which is
fairly complicated and requires initialization of memory contexts, etc.
This part of code was refactored to use a ISC_THREAD_LOCAL pointer which
greatly simplifies the whole code related to storing TLS variables.

bin/check/named-checkconf.c

@@ -709,8 +709,6 @@ main(int argc, char **argv) {
 
 	cfg_parser_destroy(&parser);
 
-	dns_name_destroy();
-
 	isc_log_destroy(&logc);
 
 	isc_mem_destroy(&mctx);