consumer: don't stop the ticker if we time out

Now that we reuse a single ticker the whole time, this would probably lead to
the consumer just kind of hanging and never resuming.

Thanks to https://github.com/Shopify/sarama/pull/1028#issuecomment-368320469 for
catching this.

consumer.go

@@ -461,7 +461,6 @@ feederLoop:
 						child.messages <- msg
 					}
 					child.broker.input <- child
-					expiryTicker.Stop()
 					continue feederLoop
 				} else {
 					// current message has not been sent, return to select