further refactor, tested, and changed master to main

tasks/finetune_utils.py

@@ -255,7 +255,7 @@ def finetune(train_valid_datasets_provider, model_provider,
         _ = load_checkpoint(model, None, None)
         args.load = original_load
         # This is critical when only model is loaded. We should make sure
-        # master parameters are also updated.
+        # main parameters are also updated.
         optimizer.reload_model_params()
     timers('pretrained checkpoint').stop()