Remove unnecessary comment about being flexible.

crates/bevy_ecs/src/system/system_registry.rs

@@ -47,7 +47,7 @@ impl World {
  ///
  /// This is different from adding systems to a [`Schedule`](crate::schedule::Schedule),
  /// because the [`SystemId`] that is returned can be used anywhere in the [`World`] to run the associated system.
- /// This allows for running systems in a pushed-based fashion, which is very flexible.
+ /// This allows for running systems in a pushed-based fashion.
  /// Using a [`Schedule`](crate::schedule::Schedule) is still preferred for most cases
  /// due to its better performance and abillity to run non-conflicting systems simultaneously.
  pub fn register_system<M, S: IntoSystem<(), (), M> + 'static>(