Remove misleading comment in docs (#5860)

Comment probably a copy/paste mistake. Removing comment as there is no "PPO-specific hyperparameters" section above.

Author: julrog

docs/Training-ML-Agents.md

@@ -277,7 +277,6 @@ behaviors:
       learning_rate_schedule: linear
 
       # PPO-specific hyperparameters
-      # Replaces the "PPO-specific hyperparameters" section above
       beta: 5.0e-3
       beta_schedule: constant
       epsilon: 0.2