clean up uses of ISC_R_NOMEMORY

the isc_mem allocation functions can no longer fail; as a result,
ISC_R_NOMEMORY is now rarely used: only when an external library
such as libjson-c or libfstrm could return NULL. (even in
these cases, arguably we should assert rather than returning
ISC_R_NOMEMORY.)

code and comments that mentioned ISC_R_NOMEMORY have been
cleaned up, and the following functions have been changed to
type void, since (in most cases) the only value they could
return was ISC_R_SUCCESS:

- dns_dns64_create()
- dns_dyndb_create()
- dns_ipkeylist_resize()
- dns_kasp_create()
- dns_kasp_key_create()
- dns_keystore_create()
- dns_order_create()
- dns_order_add()
- dns_peerlist_new()
- dns_tkeyctx_create()
- dns_view_create()
- dns_zone_setorigin()
- dns_zone_setfile()
- dns_zone_setstream()
- dns_zone_getdbtype()
- dns_zone_setjournal()
- dns_zone_setkeydirectory()
- isc_lex_openstream()
- isc_portset_create()
- isc_symtab_create()

(the exception is dns_view_create(), which could have returned
other error codes in the event of a crypto library failure when
calling isc_file_sanitize(), but that should be a RUNTIME_CHECK
anyway.)

lib/isccfg/parser.c

@@ -3797,8 +3797,8 @@ create_map(cfg_parser_t *pctx, const cfg_type_t *type, cfg_obj_t **ret) {
 	cfg_obj_t *obj = NULL;
 
 	CHECK(cfg_create_obj(pctx, type, &obj));
-	CHECK(isc_symtab_create(pctx->mctx, 5, /* XXX */
-				map_symtabitem_destroy, pctx, false, &symtab));
+	isc_symtab_create(pctx->mctx, 5, /* XXX */
+			  map_symtabitem_destroy, pctx, false, &symtab);
 	obj->value.map.symtab = symtab;
 	obj->value.map.id = NULL;