Remove 'accept dispute payout' for losing party

[drwasho]

The party that doesn't press the 'Accept Payout' button still has this button available after the counterparty presses the button transfers funds out of multisig escrow.

[drwasho]

Pressing the button doesn't do anything of course... it's more of a cleanup issue.

[drwasho]

According to Josh, the server isn't sending a message to the losing party that the dispute resolution was accepted by the winning party and funds released. This isn't a showstopper, but it would be good to clean this up later. Tagging as a v1 mainnet requirement.