config: fix litecoin simnet mode
config: fix litecoin simnet mode

This commit fixes a bug where it was impossible to run lnd in litecoin's
simnet mode because of code duplication. As a result `numNets > 1`
conditional was always true when running lnd with `cfg.Litecoin.SimNet`
flag.

aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd