multi: remove Litecoin config options

This commit removes the `Litecoin`, `LtcMode` and `LitecoindMode`
members from the main LND `Config` struct. Since only the bitcoin
blockchain is now supported, this commit also deprecates the
`cfg.Bitcoin.Active` config option.

subrpcserver_config.go

@@ -244,9 +244,6 @@ func (s *subRPCServerConfigs) PopulateDependencies(cfg *Config,
 				reflect.ValueOf(nodeSigner),
 			)
 			defaultDelta := cfg.Bitcoin.TimeLockDelta
-			if cfg.registeredChains.PrimaryChain() == chainreg.LitecoinChain {
-				defaultDelta = cfg.Litecoin.TimeLockDelta
-			}
 			subCfgValue.FieldByName("DefaultCLTVExpiry").Set(
 				reflect.ValueOf(defaultDelta),
 			)