temp fix: disable destory_process_group (#5)

When a broken world (process group) is detected, attempting to destroy
the process group causes the program to hang. We temporarily disable
this call to prevent this deadlock situation. We will revisit this later.

multiworld/world_manager.py

@@ -173,7 +173,10 @@ def remove_world(self, world_name):
         logger.debug(f"destory process group for {world_name}")
         self.set_world(world_name)
         del self._worlds[world_name]
-        dist.destroy_process_group()
+        # FIXME: calling destroy_process_group() here causes program hang.
+        #        we need to find out a right timing/way to call this function.
+        #        calling this function is temporarily disabled.
+        # dist.destroy_process_group()
         logger.debug(f"done removing world {world_name}")
 
     def set_world(self, world_name):