lnwallet: use channel type to derive keys

We abstract away how keys are generated for the different channel types
types (currently tweak(less)).

Intention is that more of the logic that is unique for each commitment
type lives in commitment.go, making the channel state machine oblivious
to the keys and outputs being created on the commitment tx for a given
channel state.

test_utils.go

@@ -195,7 +195,7 @@ func createTestPeer(notifier chainntnfs.ChainNotifier, publTx chan *wire.MsgTx,
 
 	aliceCommitTx, bobCommitTx, err := lnwallet.CreateCommitmentTxns(
 		channelBal, channelBal, &aliceCfg, &bobCfg, aliceCommitPoint,
-		bobCommitPoint, *fundingTxIn, true,
+		bobCommitPoint, *fundingTxIn, channeldb.SingleFunderTweaklessBit,
 	)
 	if err != nil {
 		return nil, nil, nil, nil, err