Clean up the simple_picking example (#15633)

## Solution

- Removed superfluous `Pickable` components
- Slightly simplified the code for updating the text color
- Removed the `Pointer<Click>` observer from the mesh entirely since
that doesn't support picking yet

examples/picking/simple_picking.rs

@@ -18,19 +18,16 @@ fn setup(
  mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
  commands
- .spawn((
- TextBundle {
- text: Text::from_section("Click Me to get a box", TextStyle::default()),
- style: Style {
- position_type: PositionType::Absolute,
- top: Val::Percent(12.0),
- left: Val::Percent(12.0),
- ..default()
- },
- ..Default::default()
+ .spawn(TextBundle {
+ text: Text::from_section("Click Me to get a box", TextStyle::default()),
+ style: Style {
+ position_type: PositionType::Absolute,
+ top: Val::Percent(12.0),
+ left: Val::Percent(12.0),
+ ..default()
  },
- Pickable::default(),
- ))
+ ..Default::default()
+ })
  .observe(
  |_click: Trigger<Pointer<Click>>,
  mut commands: Commands,
@@ -47,26 +44,18 @@ fn setup(
  )
  .observe(|evt: Trigger<Pointer<Out>>, mut texts: Query<&mut Text>| {
  let mut text = texts.get_mut(evt.entity()).unwrap();
- let first = text.sections.first_mut().unwrap();
- first.style.color = WHITE.into();
+ text.sections[0].style.color = WHITE.into();
  })
  .observe(|evt: Trigger<Pointer<Over>>, mut texts: Query<&mut Text>| {
  let mut text = texts.get_mut(evt.entity()).unwrap();
- let first = text.sections.first_mut().unwrap();
- first.style.color = BLUE.into();
+ text.sections[0].style.color = BLUE.into();
  });
  // circular base
- commands
- .spawn((
- Mesh3d(meshes.add(Circle::new(4.0))),
- MeshMaterial3d(materials.add(Color::WHITE)),
- Transform::from_rotation(Quat::from_rotation_x(-std::f32::consts::FRAC_PI_2)),
- Pickable::default(),
- ))
- .observe(|click: Trigger<Pointer<Click>>| {
- let click = click.event();
- println!("{click:?}");
- });
+ commands.spawn((
+ Mesh3d(meshes.add(Circle::new(4.0))),
+ MeshMaterial3d(materials.add(Color::WHITE)),
+ Transform::from_rotation(Quat::from_rotation_x(-std::f32::consts::FRAC_PI_2)),
+ ));
  // light
  commands.spawn((
  PointLight {