Fix shadow_biases example (#18303)

Fix moire artifacts in #16635.

Default directional light biases are overkill but it's fine.

Author: JMS55

examples/3d/shadow_biases.rs

@@ -52,14 +52,10 @@ fn setup(
                 intensity: 0.0,
                 range: spawn_plane_depth,
                 color: Color::WHITE,
-                shadow_depth_bias: 0.0,
-                shadow_normal_bias: 0.0,
                 shadows_enabled: true,
                 ..default()
             });
             builder.spawn(DirectionalLight {
-                shadow_depth_bias: 0.0,
-                shadow_normal_bias: 0.0,
                 shadows_enabled: true,
                 ..default()
             });