channel+cnct: remove preimage from channel and resolution

Now that the success resolver preimage field is always populated by the
incoming contest resolver, preimage lookups earlier in the
process (channel and channel arbitrator) can mostly be removed.

breacharbiter_test.go

@@ -1844,14 +1844,12 @@ func createInitChannels(revocationWindow int) (*lnwallet.LightningChannel, *lnwa
 		Packager:                channeldb.NewChannelPackager(shortChanID),
 	}
 
-	pCache := newMockPreimageCache()
-
 	aliceSigner := &mockSigner{aliceKeyPriv}
 	bobSigner := &mockSigner{bobKeyPriv}
 
 	alicePool := lnwallet.NewSigPool(1, aliceSigner)
 	channelAlice, err := lnwallet.NewLightningChannel(
-		aliceSigner, pCache, aliceChannelState, alicePool,
+		aliceSigner, aliceChannelState, alicePool,
 	)
 	if err != nil {
 		return nil, nil, nil, err
@@ -1860,7 +1858,7 @@ func createInitChannels(revocationWindow int) (*lnwallet.LightningChannel, *lnwa
 
 	bobPool := lnwallet.NewSigPool(1, bobSigner)
 	channelBob, err := lnwallet.NewLightningChannel(
-		bobSigner, pCache, bobChannelState, bobPool,
+		bobSigner, bobChannelState, bobPool,
 	)
 	if err != nil {
 		return nil, nil, nil, err