Remove note that is no longer true.

The code was updated to automatically handle the transaction count in the
block header without having the additional field some time ago.  This
comment was outdated.

msgblock.go

@@ -37,13 +37,6 @@ type TxLoc struct {
 // MsgBlock implements the Message interface and represents a bitcoin
 // block message.  It is used to deliver block and transaction information in
 // response to a getdata message (MsgGetData) for a given block hash.
-//
-// NOTE: Unlike the other message types which contain slices, the number of
-// transactions has a specific entry (Header.TxnCount) that must be kept in
-// sync.  The AddTransaction and ClearTransactions functions properly sync the
-// value, but if you are manually modifying the public members, you will need
-// to ensure you update the Header.TxnCount when you add and remove
-// transactions.
 type MsgBlock struct {
 	Header       BlockHeader
 	Transactions []*MsgTx