Remove PointerIsValid()

This doesn't provide any value over the standard style of checking the
pointer directly or comparing against NULL.

Also remove related:
- AllocPointerIsValid() [unused]
- IndexScanIsValid() [had one user]
- HeapScanIsValid() [unused]
- InvalidRelation [unused]

Leaving HeapTupleIsValid(), ItemIdIsValid(), PortalIsValid(),
RelationIsValid for now, to reduce code churn.

Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/ad50ab6b-6f74-4603-b099-1cd6382fb13d%40eisentraut.org
Discussion: https://www.postgresql.org/message-id/CA+hUKG+NFKnr=K4oybwDvT35dW=VAjAAfiuLxp+5JeZSOV3nBg@mail.gmail.com
Discussion: https://www.postgresql.org/message-id/bccf2803-5252-47c2-9ff0-340502d5bd1c@iki.fi

src/backend/utils/adt/acl.c

@@ -5159,7 +5159,7 @@ roles_is_member_of(Oid roleid, enum RoleRecurseType type,
 	MemoryContext oldctx;
 	bloom_filter *bf = NULL;
 
-	Assert(OidIsValid(admin_of) == PointerIsValid(admin_role));
+	Assert(OidIsValid(admin_of) == (admin_role != NULL));
 	if (admin_role != NULL)
 		*admin_role = InvalidOid;
 

src/backend/utils/adt/arrayfuncs.c

@@ -4601,7 +4601,7 @@ array_create_iterator(ArrayType *arr, int slice_ndim, ArrayMetaState *mstate)
 	/*
 	 * Sanity-check inputs --- caller should have got this right already
 	 */
-	Assert(PointerIsValid(arr));
+	Assert(arr);
 	if (slice_ndim < 0 || slice_ndim > ARR_NDIM(arr))
 		elog(ERROR, "invalid arguments to array_create_iterator");
 

src/backend/utils/adt/datum.c

@@ -84,7 +84,7 @@ datumGetSize(Datum value, bool typByVal, int typLen)
 			/* It is a varlena datatype */
 			struct varlena *s = (struct varlena *) DatumGetPointer(value);
 
-			if (!PointerIsValid(s))
+			if (!s)
 				ereport(ERROR,
 						(errcode(ERRCODE_DATA_EXCEPTION),
 						 errmsg("invalid Datum pointer")));
@@ -96,7 +96,7 @@ datumGetSize(Datum value, bool typByVal, int typLen)
 			/* It is a cstring datatype */
 			char	   *s = (char *) DatumGetPointer(value);
 
-			if (!PointerIsValid(s))
+			if (!s)
 				ereport(ERROR,
 						(errcode(ERRCODE_DATA_EXCEPTION),
 						 errmsg("invalid Datum pointer")));

src/backend/utils/adt/xml.c

@@ -4895,7 +4895,7 @@ XmlTableSetColumnFilter(TableFuncScanState *state, const char *path, int colnum)
 	XmlTableBuilderData *xtCxt;
 	xmlChar    *xstr;
 
-	Assert(PointerIsValid(path));
+	Assert(path);
 
 	xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableSetColumnFilter");