lnwallet: simplify remote balance computation for single funder
lnwallet: simplify remote balance computation for single funder

The remote balance in the case of a single funder workflow is simply
what ever the pushSat amount is. The capacity - fundingAmt in this
scenario would always be zero, so we simply just set it directly to
pushSat.

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