Fix leakage of memory context header in find_all_inheritors().

Commit 827d6f97 contained the same misunderstanding of hash_create's API
as commit 090010f2.  As in 5d00b764, remove the unnecessary layer of
memory context.  (This bug is less significant than the other one, since
the extra context would be under a relatively short-lived context, but
it's still a bug.)

src/backend/catalog/pg_inherits.c

@@ -29,9 +29,9 @@
 #include "storage/lmgr.h"
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
+#include "utils/memutils.h"
 #include "utils/syscache.h"
 #include "utils/tqual.h"
-#include "utils/memutils.h"
 
 /*
  * Entry of a hash table used in find_all_inheritors. See below.
@@ -169,29 +169,19 @@ find_all_inheritors(Oid parentrelId, LOCKMODE lockmode, List **numparents)
 	/* hash table for O(1) rel_oid -> rel_numparents cell lookup */
 	HTAB		   *seen_rels;
 	HASHCTL			ctl;
-	MemoryContext	new_ctx;
 	List	   *rels_list,
 			   *rel_numparents;
 	ListCell   *l;
 
-	/*
-	 * We need a separate memory context for a hash table. This is because
-	 * hash table is used only in this procedure. To free a memory we need to
-	 * call hash_destroy which is just a wrapper around MemoryContextDelete.
-	 */
-	new_ctx = AllocSetContextCreate(CurrentMemoryContext,
-									"FindAllInheritorsSeenRelsContext",
-									ALLOCSET_DEFAULT_SIZES);
-
 	memset(&ctl, 0, sizeof(ctl));
 	ctl.keysize = sizeof(Oid);
 	ctl.entrysize = sizeof(SeenRelsEntry);
-	ctl.hcxt = new_ctx;
+	ctl.hcxt = CurrentMemoryContext;
 
-	seen_rels = hash_create(
-		"find_all_inheritors temporary table",
-		32, /* start small and extend */
-		&ctl, HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+	seen_rels = hash_create("find_all_inheritors temporary table",
+							32, /* start small and extend */
+							&ctl,
+							HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 
 	/*
 	 * We build a list starting with the given rel and adding all direct and