Remove bad panic in coordinator

It expected ConfirmationShare to be n-of-n, not t-of-n.

coordinator/src/tributary/handle.rs

@@ -359,10 +359,7 @@ impl<
               )
               .await;
           }
-          Accumulation::Ready(DataSet::NotParticipating) => {
-            panic!("wasn't a participant in DKG confirmination shares")
-          }
-          Accumulation::NotReady => {}
+          Accumulation::Ready(DataSet::NotParticipating) | Accumulation::NotReady => {}
         }
       }