Removing a readable listener now updates the readable state i.e.
Replicates changes made in joyent/node's PR: https://github.com/joyent/node/pull/25886
readableListening, needReadable and emittedReadable are set to false. Then, if a readable listener is added at a later time, the stream will know none are attached and will take proper action to get the stream going back again.
Fixes joyent/node#7678