Correct processor flow to have the coordinator decide signing set/re-attempts

The signing set should be the first group to submit preprocesses to Tributary.
Re-attempts shouldn't be once every 30s, yet n blocks since the last relevant
message.

Removes the use of an async task/channel in the signer (and Substrate signer).
Also removes the need to be able to get the time from a coin's block, which was
a fragile system marked with a TODO already.

processor/messages/Cargo.toml

@@ -16,10 +16,6 @@ rustdoc-args = ["--cfg", "docsrs"]
 [dependencies]
 zeroize = { version = "1", features = ["derive"] }
 
-rand_core = "0.6"
-rand_chacha = "0.3"
-transcript = { package = "flexible-transcript", path = "../../crypto/transcript" }
-
 serde = { version = "1", features = ["derive"] }
 
 dkg = { path = "../../crypto/dkg", features = ["serde"] }