remove callback checks where callback is required
remove callback checks where callback is required

nseckinoral/node-steam-tradeoffers,lpinca/node-steam-tradeoffers,vejbuch/node-steam-tradeoffers,GoeGaming/node-steam-tradeoffers,FelikZ/node-steam-tradeoffer-manager,Alex7Kom/node-steam-tradeoffers,LorienMan/node-steam-tradeoffers