channeldb: reset database version back to zero
channeldb: reset database version back to zero

As we removed the prior migration in an earlier commit, we now reset
the version of the database back to zero (no migrations needed).

ddustin/lnd,LightningNetwork/lnd,LightningNetwork/lnd,AndrewSamokhvalov/lnd,AndrewSamokhvalov/lnd,aakselrod/lnd,aakselrod/lnd,ddustin/lnd