Delete open_instruct/ppo2.py (#1130)

* Delete open_instruct/ppo2.py

* deleted all mentions of ppo_fast.py

Author: finbarrtimbers

mason.py

@@ -23,9 +23,8 @@
     "open_instruct/finetune.py",
     "open_instruct/dpo_tune_cache.py",
     "open_instruct/grpo_fast.py",
-    "open_instruct/ppo_fast.py",
+    "open_instruct/ppo.py",
     "open_instruct/grpo_vllm_thread_ray_gtrl.py",
-    "open_instruct/ppo2.py",
     "open_instruct/ppo_vllm_thread_ray_gtrl.py",
     "open_instruct/reward_modeling.py",
 ]