Enable physics interpolation in all 2D demos (#1070)

This makes uses of the new built-in 2D physics interpolation
added in 4.3.

For 3D demos, a separate PR requiring `master` will be made later.

2d/hexagonal_map/project.godot

@@ -64,6 +64,7 @@ move_up={
 [physics]
 
 common/physics_ticks_per_second=120
+common/physics_interpolation=true
 
 [rendering]
 

2d/hexagonal_map/troll.tscn

@@ -25,3 +25,4 @@ position = Vector2(3.24216, 19.453)
 shape = SubResource("1")
 
 [node name="Camera2D" type="Camera2D" parent="."]
+process_callback = 0