Skip pg_catalog Oid lookup

pg_catalog Oid is hardcoded in postgres so we can skip the lookup
and instead use PG_CATALOG_NAMESPACE

Author: svenklemm

src/func_cache.c

@@ -537,7 +537,6 @@ initialize_func_info()
 	};
 	Oid extension_nsp = ts_extension_schema_oid();
 	Oid experimental_nsp = get_namespace_oid(ts_experimental_schema_name(), false);
-	Oid pg_nsp = get_namespace_oid("pg_catalog", false);
 	HeapTuple tuple;
 	Relation rel;
 
@@ -551,7 +550,7 @@ initialize_func_info()
 	for (size_t i = 0; i < _MAX_CACHE_FUNCTIONS; i++)
 	{
 		FuncInfo *finfo = &funcinfo[i];
-		Oid namespaceoid = pg_nsp;
+		Oid namespaceoid = PG_CATALOG_NAMESPACE;
 		oidvector *paramtypes = buildoidvector(finfo->arg_types, finfo->nargs);
 		FuncEntry *fentry;
 		bool hash_found;