Remove unnecessary compute for rotation interpolation (#14019)

# Objective

- `slerp` has a built-in short path check. And quaternions are ensured
to be normalized during loading .

## Solution
- remove it 

## Testing
`many_foxes ` in single thread

![image](https://github.com/bevyengine/bevy/assets/45868716/a7e74050-e202-4adb-9179-82a87263c300)

crates/bevy_animation/src/lib.rs

@@ -957,13 +957,10 @@ impl AnimationTargetContext<'_> {
                 };
 
                 let rot_start = keyframes[step_start];
-                let mut rot_end = keyframes[step_start + 1];
-                // Choose the smallest angle for the rotation
-                if rot_end.dot(rot_start) < 0.0 {
-                    rot_end = -rot_end;
-                }
+                let rot_end = keyframes[step_start + 1];
+
                 // Rotations are using a spherical linear interpolation
-                let rot = rot_start.normalize().slerp(rot_end.normalize(), lerp);
+                let rot = rot_start.slerp(rot_end, lerp);
                 transform.rotation = transform.rotation.slerp(rot, weight);
             }