ilp pay: deprecate application level data

[matdehaast]

Currently ilp-pay does lots of stuff that is specific to SPSP & Open payments. For Rafiki this makes it tricky to use ilp-pay as you have to fight with the pushing Open payments level logic into ilp-pay and syncing between the two repos.

I propose we remove all application level logic from ilp-pay and rather just leave it as having the quote and send functionility where you just pass in the required level of information to do that.