Android 4.4 and later support a mode where all the on-screen buttons are hidden. Better late than never, I guess.
I experimented with it a few times, but with the old engine the support was really brittle and the game was doing strange things for no reason.
No so with the new Engine. See the photo of my trusty Nexus 5:
Yes, no buttons. Totally full screen. You need at least KitKat (Android 4.4) device for this to work, otherwise you’ll get the buttons.
By the way, the awesome world on the screenshot is called “Mansions” and you can find it in Community Content (you need to go to recently added, and click “more items” about 20 times or so).