<iframe width="100%" height="100%" src="//www.youtube.com/embed/qUJYqhKZrwA?autoplay=1&showinfo=0&controls=0" frameborder="0" allowfullscreen>
If you remove ?autoplay=1 the video does not work. Looks like you cannot use the controls parameter without autoplay enabled.
Not sure why this is not mentioned in the YouTube embed writeup.
Hope I'm wrong.
https://developers.google.com/youtube/player_parameters#controls
You can hide the "Watch Later" Button by using "Youtube-nocookie" (this will not hide the share Button)
Adding controls=0 will also remove the video control bar at the bottom of the screen and using modestbranding=1 will remove the youtube logo at bottom right of the screen
However using them both doesn't works as expected (it only hides the video control bar)
<iframe width="100%" height="100%" src="https://www.youtube-nocookie.com/embed/fNb-DTEb43M?controls=0" frameborder="0" allowfullscreen></iframe>