Revert coordinator/tributary to fd4f247917

\#560 is causing notable CI failures, with its logs including slashes at 10x
the prior rate.

coordinator/tributary/tendermint/tests/ext.rs

@@ -145,7 +145,7 @@ impl Network for TestNetwork {
     println!("Slash for {id} due to {event:?}");
   }
 
-  async fn validate(&self, block: &TestBlock) -> Result<(), BlockError> {
+  async fn validate(&mut self, block: &TestBlock) -> Result<(), BlockError> {
     block.valid
   }