This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules
This commit removes the context as a param needed when calling methods
of HarnessNode. This change moves the context management inside
HarnessNode, aside from saving us a few lines, it makes the context
creation/timeout less error-prone.
This permits an AMP invoice to be "pseudo-reusable", where the invoice
paramters can be used multiple times so long as a new payment address is
supplied. This prevents additional round trips between payer and payee
to obtain a new invoice, even though the payments/invoices won't be
logically associated via the RPC interface like they would when the full
reusable invoices are deployed.
