sauron: fix fee response or deprecate the plugin

[vincenzopalazzo]

In the next release, there is a cleanup that breaks sauron and I think trusted coin, so we should consider fixing it or archiving.

Related commit: ElementsProject/lightning@82c1d8b

P.S: a modern alternative of this is Folgore https://github.com/coffee-tools/folgore if we ran out of alternative backend

[vincenzopalazzo]

Duplicated #458

[chrisguida]

@vincenzopalazzo is folgore a plugin? should we add it in here?

[vincenzopalazzo]

yes folgore is a plugin. not sure if we need to add it here, keep update the submodule is a little bit hard

[chrisguida]

If it's a plugin, I say we add it here! This should be a collection of all useful, actively maintained plugins.