make the examples use the States derive macro (#8289)

# Objective
Some examples still manually implement the States trait, even though
manual implementation is no longer needed as there is now the derive
macro for that.

---------

Signed-off-by: Natalia Asteria <fortressnordlys@outlook.com>

examples/2d/texture_atlas.rs

@@ -14,21 +14,13 @@ fn main() {
         .run();
 }
 
-#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash, States)]
 enum AppState {
     #[default]
     Setup,
     Finished,
 }
 
-impl States for AppState {
-    type Iter = std::array::IntoIter<AppState, 2>;
-
-    fn variants() -> Self::Iter {
-        [AppState::Setup, AppState::Finished].into_iter()
-    }
-}
-
 #[derive(Resource, Default)]
 struct RpgSpriteHandles {
     handles: Vec<HandleUntyped>,

examples/ecs/generic_system.rs

@@ -11,21 +11,13 @@
 
 use bevy::prelude::*;
 
-#[derive(Debug, Default, Clone, Copy, Eq, PartialEq, Hash)]
+#[derive(Debug, Default, Clone, Copy, Eq, PartialEq, Hash, States)]
 enum AppState {
     #[default]
     MainMenu,
     InGame,
 }
 
-impl States for AppState {
-    type Iter = std::array::IntoIter<AppState, 2>;
-
-    fn variants() -> Self::Iter {
-        [AppState::MainMenu, AppState::InGame].into_iter()
-    }
-}
-
 #[derive(Component)]
 struct TextToPrint(String);