Remove heap_fetch_extended function.

Sync src/backend/access/heap/heapam.c internals with upstream.

heap_fetch_extended introudced postgres/postgres@c590e51
as back-paches fix from HEAD. There is no point to keep this function
after postgresql-16 merge

Author: reshke

src/backend/access/heap/heapam.c

@@ -1424,25 +1424,6 @@ heap_fetch(Relation relation,
 		   HeapTuple tuple,
 		   Buffer *userbuf,
 		   bool keep_buf)
-{
-	return heap_fetch_extended(relation, snapshot, tuple, userbuf, false);
-}
-
-/*
- *	heap_fetch_extended		- fetch tuple even if it fails snapshot test
- *
- * If keep_buf is true, then upon finding a tuple that is valid but fails
- * the snapshot check, we return the tuple pointer in tuple->t_data and the
- * buffer ID in *userbuf, keeping the buffer pin, just as if it had passed
- * the snapshot.  (The function result is still "false" though.)
- * If keep_buf is false then this behaves identically to heap_fetch().
- */
-bool
-heap_fetch_extended(Relation relation,
-					Snapshot snapshot,
-					HeapTuple tuple,
-					Buffer *userbuf,
-					bool keep_buf)
 {
 	ItemPointer tid = &(tuple->t_self);
 	ItemId		lp;

src/include/access/heapam.h

@@ -229,9 +229,6 @@ extern bool heap_getnextslot_tidrange(TableScanDesc sscan,
 extern uint32 heap_scan_flags(Relation relation);
 extern bool heap_fetch(Relation relation, Snapshot snapshot,
 					   HeapTuple tuple, Buffer *userbuf, bool keep_buf);
-extern bool heap_fetch_extended(Relation relation, Snapshot snapshot,
-								HeapTuple tuple, Buffer *userbuf,
-								bool keep_buf);
 extern bool heap_hot_search_buffer(ItemPointer tid, Relation relation,
 								   Buffer buffer, Snapshot snapshot, HeapTuple heapTuple,
 								   bool *all_dead, bool first_call);