Revert "add plane below the player"

This reverts commit 57e5241abf.

src/world.rs

@@ -58,13 +58,6 @@ pub fn setup(
         ..default()
     });
 
-    commands.spawn(PbrBundle {
-        mesh: meshes.add(Plane3d::default().mesh().size(20.0, 20.0)),
-        transform: Transform::from_xyz(0.0, -20.0, 0.0),
-        material: white_handle,
-        ..default()
-    });
-
     // Space is DARK
     ambient_light.brightness = 0.0;