channeldb: remove obsolete idKey methods
channeldb: remove obsolete idKey methods

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