Remove references to frustrum culling in 2d tests

Since the new renderer, no frustrum culling is applied to 2d components
(be it Sprite or Mesh2d), the stress_tests docs is therefore misleading
and should be updated.

examples/stress_tests/many_animated_sprites.rs

@@ -1,8 +1,5 @@
 //! Renders a lot of animated sprites to allow performance testing.
 //!
-//! It sets up many animated sprites in different sizes and rotations, and at different scales in the world,
-//! and moves the camera over them to see how well frustum culling works.
-//!
 //! To measure performance realistically, be sure to run this in release mode.
 //! `cargo run --example many_animated_sprites --release`
 

examples/stress_tests/many_sprites.rs

@@ -1,9 +1,6 @@
 //! Renders a lot of sprites to allow performance testing.
 //! See <https://github.com/bevyengine/bevy/pull/1492>
 //!
-//! It sets up many sprites in different sizes and rotations, and at different scales in the world,
-//! and moves the camera over them to see how well frustum culling works.
-//!
 //! Add the `--colored` arg to run with color tinted sprites. This will cause the sprites to be rendered
 //! in multiple batches, reducing performance but useful for testing.