We remove the auxiliary RPC renesenday (only used internally) in favor
of a function that builds the onion, stores the shared secrets
needed to recover the onion reply, and calls sendonion/injectpaymentonion.
This solves a concurrency race
```
**BROKEN** plugin-cln-renepay: Unable to parse sendpay_failure
```
in which we are waiting for renesenday to return in order to record the shared
secrets but we get the a sendpay_failure notification with an onionreply
before we have secrets to decode it.
It also solves a missing JSON id seen in the logs
```
DEBUG plugin-cln-renepay: JSON reply with unknown id
```
because renesendpay was using his command variable to issue an RPC
to sendonion/injecpaymentonion and would fail or succeed the command
before those RPCs were done. This also meant that the callback
functions were silently being ignored.
Changelog-Fixed: renepay: fixes a race condition that leads to **BROKEN** plugin-cln-renepay: Unable to parse sendpay_failure
Signed-off-by: Lagrang3 <lagrang3@protonmail.com>
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580c2f7854