sprites: Just convert the enum to an integer directly

No match needed, for simple enums one can just convert them to their
integer discriminant with `as <int-type>`.

src/sprites.rs

@@ -29,8 +29,6 @@ impl Sprite {
 
 impl Into<resources::ImageHandle> for Sprite {
     fn into(self) -> resources::ImageHandle {
-        resources::ImageHandle(match self {
-            Sprite::Player => 1,
-        })
+        resources::ImageHandle(self as usize)
     }
 }