This reverts commit 17da2ba7fa691c666d70948217ffcd5b6ac148f8.
This was done prematurely. This will be revisited when a code
restructure is more urgent.
This change moves IsFinalizedTransaction to txscript and also changes
the first argument to take a wire.MsgTx instead of btcutil.Tx. This
is needed for an upcoming diff in which txscript will require
IsFinalizedTransaction and we do not want to import the btcd/blockchain.