Remove all_paths_failed from PaymentPathFailed

Remove all_paths_failed from PaymentPathFailed

This field was previous useful in manual retries for users to know when all
paths of a payment have failed and it is safe to retry. Now that we support
automatic retries in ChannelManager and no longer support manual retries, the
field is no longer useful.

For backwards compat, we now always write false for this field. If we didn't do
this, previous versions would default this field's value to true, which can be
problematic because some clients have relied on the field to indicate when a
full payment retry is safe.