Replace panic!() with unreachable!()

src/service/rooms/timeline/mod.rs

@@ -407,7 +407,7 @@ impl Service {
                             self.redact_pdu(redact_id, pdu)?;
                         }
                     }
-                    _ => panic!("Unexpected room version {}", room_version_id)
+                    _ => unreachable!("Validity of room version already checked")
                 };
             }
             TimelineEventType::SpaceChild => {