lnwallet: eliminate flaky assert within integration tests
lnwallet: eliminate flaky assert within integration tests

This commit removes a flaky assertion within the interaction tests. Due
to differences in final coin selection across tests due to the
pseudo-random nature of map iterations, a single output might be
selected rather than two as we previously expected.

Additionally a duplicate test has been removed, and the locked output tests
simplified a bit.

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