message: dfa: remove some redundant branches
  I discovered these while reviewing the code to prep for the rewrite
  in regex-automata.
diff: @@ -1353,7 +1353,6 @@ impl<'a> Fsm<'a> {
  match self.cache.trans.next(si, self.byte_class(b)) {
  STATE_UNKNOWN => self.exec_byte(qcur, qnext, si, b),
  STATE_QUIT => None,
  - STATE_DEAD => Some(STATE_DEAD),
  nsi => Some(nsi),
  }
  }
  @@ -1387,7 +1386,6 @@ impl<'a> Fsm<'a> {
  };
  match self.cache.start_states[flagi] {
  STATE_UNKNOWN => {}
  - STATE_DEAD => return Some(STATE_DEAD),
  si => return Some(si),
  }
  q.clear();
  