Remove fake invoice generation

[benthecarman]

This would cause the zap event we create to not be the same for every invoice because we would randomly generate the fake invoice. The fake invoice part of the zap recipient was mostly a gimmick, this just uses the actual invoice so we can have determinism that way the zap recipient will always be the same even if it is generated multiple times

[TonyGiorgio]

fake invoice part of the zap recipient was mostly a gimmick

I would like to better understand why this was done at all.

[benthecarman]

Slightly better privacy so we don't broadcast the gateway that was used. Doesn't really give much though because you can always just call the lightning address to get an invoice and see