Remove HeapTupleheaderSetXminCommitted/Invalid functions

Reasons include: (1). They are not used in core or any known
third-party extension in codesearch.debian.net. (2). They are not safe
to use when comparing with HeapTupleSetHintBits which is a public API
as well for third party. (3). These functions do has some maintenance
cost when people try to understanding them,  including identifying they
are not used at all and the right one is SetHintBits.

Discussion:
https://www.postgresql.org/message-id/87frfmgigm.fsf%40163.com

Author: Andy Fan

src/include/access/htup_details.h

@@ -357,20 +357,6 @@ HeapTupleHeaderXminFrozen(const HeapTupleHeaderData *tup)
 	return (tup->t_infomask & HEAP_XMIN_FROZEN) == HEAP_XMIN_FROZEN;
 }
 
-static inline void
-HeapTupleHeaderSetXminCommitted(HeapTupleHeaderData *tup)
-{
-	Assert(!HeapTupleHeaderXminInvalid(tup));
-	tup->t_infomask |= HEAP_XMIN_COMMITTED;
-}
-
-static inline void
-HeapTupleHeaderSetXminInvalid(HeapTupleHeaderData *tup)
-{
-	Assert(!HeapTupleHeaderXminCommitted(tup));
-	tup->t_infomask |= HEAP_XMIN_INVALID;
-}
-
 static inline void
 HeapTupleHeaderSetXminFrozen(HeapTupleHeaderData *tup)
 {