How do I remove optional tasks from my task list?
You can't actually remove the optional tasks from your task list, but you don't have to do them to continue progressing in the game. The reason they don't disappear is in case you decide you want to do them later. Keep in mind you can earn 2 coins every time you level up by posting to Facebook and Twitter. Also, there are special tasks that pop up from time to time that award coins as well.