Remove _ignored_param_names (#91530)
'_ignored_param_names' is only used in 'param_hook' during state_dict() post hook processing to check a parameter key needs to be cloned or not. But it is not needed, as state_dict() post hook only passes fsdp managed parameter keys to 'param_hook', see https://github.com/pytorch/pytorch/blob/master/torch/distributed/fsdp/_state_dict_utils.py#L203. That means the passed parameter keys are always not part of '_ignored_param_names'.
so we should be able to safely remove '_ignored_param_names' and related codes
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91530
Approved by: https://github.com/rohan-varma
