Fix `go vet` errors.

broker.go

@@ -232,8 +232,6 @@ func (b *Broker) sendAndReceive(clientID string, req requestEncoder, res decoder
 	case err = <-promise.errors:
 		return err
 	}
-
-	return nil
 }
 
 func (b *Broker) decode(pd packetDecoder) (err error) {

consumer.go

@@ -168,8 +168,6 @@ func (c *Consumer) sendError(err error) bool {
 	case c.events <- &ConsumerEvent{Err: err}:
 		return true
 	}
-
-	return true
 }
 
 func (c *Consumer) fetchMessages() {