Remove Internal Routing

[karlb]

Problems With Internal Routing

• Does not know about fee schedule. It currently always assumes 2% fees for the whole payment, which is expensive, but can still be too low in some cases
• Forces the client to build a representation of the whole network. This makes syncing the raiden client on mainnet at startup horrible slow (See Reduce time for initial sync by providing a JSON #6209).
• Current implementation has several limitations. Better implemantations would duplicate more code from the PFS.
• Existing problems will only grow bigger with new features (e.g. better support for token swaps)
• Not tested in SP
• Not manually tested on Alderaan release

Todos

Due to these problems, it is better to remove the internal routing and rely on the PFS for payments through non-direct channels.

• Provide way to do non-direct payments in integration test without internal routing (give routes explicitly?)
• Remove usage of internal routing from tests (delete test that are only about testing the internal routing)
• Remove internal routing from CLI flags and documentation
• Remove internal routing code

Followups

• More selective filters during startup Faster syncing during startup by more selective filtering #6497