No longer need to ignore downstream send errors

By removing the exit variables, the downstream stages wait for
upstream stages to drop their senders before exiting.

src/banking_stage.rs

@@ -48,7 +48,6 @@ impl BankingStage {
                     match e {
                         Error::RecvTimeoutError(RecvTimeoutError::Disconnected) => break,
                         Error::RecvTimeoutError(RecvTimeoutError::Timeout) => (),
-                        Error::SendError => (), // Ignore when downstream stage exits prematurely.
                         _ => error!("{:?}", e),
                     }
                 }

src/write_stage.rs

@@ -64,7 +64,6 @@ impl WriteStage {
                         match e {
                             Error::RecvTimeoutError(RecvTimeoutError::Disconnected) => break,
                             Error::RecvTimeoutError(RecvTimeoutError::Timeout) => (),
-                            Error::SendError => (), // Ignore when downstream stage exits prematurely.
                             _ => error!("{:?}", e),
                         }
                     };