askrene: askrene-remove-channel-update

[Lagrang3]

Add a new RPC askrene-remove-channel-update to remove channel_update entries from layers.

[cdecker]

Is the intention here to undo an update that was applied or to make that direction unusable? The implementation does the latter, though you can just feed in any prior update and re-enable it with those params again.

[daywalker90]

I assume this is in line with the other askrene commands and we want it in cln-grpc etc.:

If so, please:

1. add AskRene-Remove-Channel-Update to grpc_method_names in contrib/msggen/msggen/utils/utils.py
2. run uv run make gen.

If that doesn't generate anything you should try touch ‎doc/schemas/askrene-remove-channel-update.json first and then 2. again.

[Lagrang3]

Is the intention here to undo an update that was applied or to make that direction unusable? The implementation does the latter, though you can just feed in any prior update and re-enable it with those params again.

These entries override the channel properties we get from gossip.
I just want to be able to remove the entry from the list when it is no longer needed.

[cdecker]

Rebased on top of master. Ready to merge when green.