Fix canceling subscription

Author: haadcode

src/core/components/pubsub.js

@@ -47,7 +47,11 @@ module.exports = function pubsub (self) {
 
       // There is no explicit unsubscribe; subscriptions have a cancel event
       stream.cancel = promisify((cb) => {
+        // Remove the event listener
+        self._pubsub.removeAllListeners(topic)
+        // Make sure floodsub knows we've unsubscribed
         self._pubsub.unsubscribe(topic)
+        // Remove the subscription from pubsub's internal state
         removeSubscription(topic, cb)
       })