Clean up FIXME added after WINDOW merge

These underlying issues  where resolved in the following PRs that were
merged. The fixmes where not removed.

https://github.com/greenplum-db/gpdb/pull/4174/files
https://github.com/greenplum-db/gporca/pull/263

src/backend/gpopt/translate/CTranslatorDXLToScalar.cpp

@@ -547,22 +547,6 @@ CTranslatorDXLToScalar::PwindowrefFromDXLNodeScWindowRef
 	WindowFunc *pwindowfunc = MakeNode(WindowFunc);
 	pwindowfunc->winfnoid = CMDIdGPDB::PmdidConvert(pdxlop->PmdidFunc())->OidObjectId();
 
-	// GPDB_84_MERGE_FIXME: The OIDS of a few built-in window
-	// functions have been hard-coded in ORCA. But the OIDs
-	// were changed when we merged the upstream window function
-	// implementation, to match the upstream OIDs. Map the old
-	// OIDs to the upstream ones.
-	if (pwindowfunc->winfnoid == 7000)	// ROW_NUMBER()
-		pwindowfunc->winfnoid = 3100;
-	if (pwindowfunc->winfnoid == 7002)	// DENSE_RANK()
-		pwindowfunc->winfnoid = 3102;
-	if (pwindowfunc->winfnoid == 7003)	// PERCENT_RANK()
-		pwindowfunc->winfnoid = 3103;
-	if (pwindowfunc->winfnoid == 7004)	// CUME_DIST()
-		pwindowfunc->winfnoid = 3104;
-	if (pwindowfunc->winfnoid == 7005)	// NTILE(int4)
-		pwindowfunc->winfnoid = 3105;
-
 	pwindowfunc->windistinct = pdxlop->FDistinct();
 	pwindowfunc->location = -1;
 	pwindowfunc->winref = pdxlop->UlWinSpecPos() + 1;

src/backend/gpopt/translate/CTranslatorRelcacheToDXL.cpp

@@ -164,22 +164,6 @@ CTranslatorRelcacheToDXL::PimdobjGPDB
 
 	OID oid = CMDIdGPDB::PmdidConvert(pmdid)->OidObjectId();
 
-	// GPDB_84_MERGE_FIXME: The OIDS of a few built-in window
-	// functions have been hard-coded in ORCA. But the OIDs
-	// were changed when we merged the upstream window function
-	// implementation, to match the upstream OIDs. Map the old
-	// OIDs to the upstream ones.
-	if (oid == 7000)	// ROW_NUMBER()
-		oid = 3100;
-	if (oid == 7002)	// DENSE_RANK()
-		oid = 3102;
-	if (oid == 7003)	// PERCENT_RANK()
-		oid = 3103;
-	if (oid == 7004)	// CUME_DIST()
-		oid = 3104;
-	if (oid == 7005)	// NTILE(int4)
-		oid = 3105;
-
 	GPOS_ASSERT(0 != oid);
 
 	// find out what type of object this oid stands for
@@ -1836,23 +1820,6 @@ CTranslatorRelcacheToDXL::Pmdfunc
 {
 	OID oidFunc = CMDIdGPDB::PmdidConvert(pmdid)->OidObjectId();
 
-
-	// GPDB_84_MERGE_FIXME: The OIDS of a few built-in window
-	// functions have been hard-coded in ORCA. But the OIDs
-	// were changed when we merged the upstream window function
-	// implementation, to match the upstream OIDs. Map the old
-	// OIDs to the upstream ones.
-	if (oidFunc == 7000)	// ROW_NUMBER()
-		oidFunc = 3100;
-	if (oidFunc == 7002)	// DENSE_RANK()
-		oidFunc = 3102;
-	if (oidFunc == 7003)	// PERCENT_RANK()
-		oidFunc = 3103;
-	if (oidFunc == 7004)	// CUME_DIST()
-		oidFunc = 3104;
-	if (oidFunc == 7005)	// NTILE(int4)
-		oidFunc = 3105;
-
 	GPOS_ASSERT(InvalidOid != oidFunc);
 
 	// get func name