[bug-fix] Disable threading for self-play envs (#4679)

config/ppo/SoccerTwos.yaml

     max_steps: 50000000
     time_horizon: 1000
     summary_freq: 10000
-    threaded: true
+    threaded: false
     self_play:
       save_steps: 50000
       team_change: 200000

config/ppo/StrikersVsGoalie.yaml

     max_steps: 30000000
     time_horizon: 1000
     summary_freq: 10000
-    threaded: true
+    threaded: false
     self_play:
       save_steps: 50000
       team_change: 200000
     max_steps: 30000000
     time_horizon: 1000
     summary_freq: 10000
-    threaded: true
+    threaded: false
     self_play:
       save_steps: 50000
       team_change: 200000

config/ppo/Tennis.yaml

     max_steps: 50000000
     time_horizon: 1000
     summary_freq: 10000
-    threaded: true
+    threaded: false
     self_play:
       save_steps: 50000
       team_change: 100000