[short_path] Delete next_J in compute_cost_to_go

Author: Eri-Oyama

lectures/short_path.md

@@ -429,7 +429,6 @@ def bellman(J, Q):
 
 def compute_cost_to_go(Q):
     J = np.zeros(num_nodes)      # Initial guess
-    next_J = np.empty(num_nodes)  # Stores updated guess
     max_iter = 500
     i = 0