remove note about validity copied from non unchecked_mut variant

crates/bevy_ecs/src/world/entity_ref.rs

@@ -136,7 +136,7 @@ impl<'w> EntityRef<'w> {
     /// compile time.**
     ///
     /// Unlike [`EntityRef::get`], this returns a raw pointer to the component,
-    /// which is only valid while the `'w` borrow of the lifetime is active.
+    /// instead of a reference.
     ///
     /// # Safety
     ///