Remove spurious code comments in standby related code

GetRunningTransactionData() suggested that subxids were not worth
optimizing away if overflowed, yet they have already been removed
for that case.

Changes to LogAccessExclusiveLock() API forgot to remove the
prior comment when it was copied to LockAcquire().

Author: simonat2ndQuadrant

src/backend/storage/ipc/procarray.c

@@ -1926,9 +1926,7 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
  * that bookkeeping.
  *
  * Note that if any transaction has overflowed its cached subtransactions
- * then there is no real need include any subtransactions. That isn't a
- * common enough case to worry about optimising the size of the WAL record,
- * and we may wish to see that data for diagnostic purposes anyway.
+ * then there is no real need include any subtransactions.
  */
 RunningTransactions
 GetRunningTransactionData(void)

src/backend/storage/ipc/standby.c

@@ -1050,11 +1050,6 @@ LogAccessExclusiveLock(Oid dbOid, Oid relOid)
 
 	xlrec.xid = GetCurrentTransactionId();
 
-	/*
-	 * Decode the locktag back to the original values, to avoid sending lots
-	 * of empty bytes with every message.  See lock.h to check how a locktag
-	 * is defined for LOCKTAG_RELATION
-	 */
 	xlrec.dbOid = dbOid;
 	xlrec.relOid = relOid;