MTG - Minetest Game is the game. It's in the name. Delete it, and you cannot play Minetest. Minetest is referred to as the engine. They renamed MTG and put it into maintenance mode because of the confusion. It was badly named initially. The team have already made the decision to remove MTG by default so it comes with no games. They are just waiting to redevelop the UI so it isn't so painful when this happens.