fix(changestream): removes all event listeners on close

Fixes Node-1727

Author: Rosemary Yin

lib/change_stream.js

@@ -154,6 +154,7 @@ class ChangeStream extends EventEmitter {
 
     // Tidy up the existing cursor
     var cursor = this.cursor;
+    ['data', 'close', 'end', 'error'].forEach(event => this.cursor.removeAllListeners(event));
     delete this.cursor;
     return cursor.close(callback);
   }