MNT: Update flight.py to remove duplicate line

Co-authored-by: Gui-FernandesBR <[email protected]>

Author: aZira371

rocketpy/simulation/flight.py

@@ -2160,7 +2160,6 @@ def u_dot_parachute(self, t, u, post_processing=False):
         #     (1 - eta) * t**5 + eta * (to**3) * (t**2)
         # )
         # Rdot = 0
-        # tf = 8 * nominal diameter / velocity at line stretch
 
         # tf = 8 * nominal diameter / velocity at line stretch