[readability] Consolidate prune_heads logic to PretrainedModel.
Many models have identical implementations of `prune_heads` it would be nice to store that implementation as a method on `PretrainedModel` and reduce the redundancy.
Hi @sshleifer , 
I am new to opensource and would like to help out with this issue. Could you please point me to some guide to setting up the project locally.
Thanks.<|||||>I got the contributing.md file. Thanks anyways. :)<|||||>Hi @sshleifer 
I am looking for a contribution. Is the issue is still open?
Thanks and Regards<|||||>@Shandilya21 It looks open. I was trying to work on it and got stuck at a point. Do let me know if you would like to discuss<|||||>Hi @noelmat Okay, can you tell me where you got stuck? I am happy to discuss this.<|||||>Is anybody working on this? I'm new to open source but I'd like to give it a shot<|||||>Go for it!<|||||>> Is anybody working on this? I'm new to open source but I'd like to give it a shot

Yeah, I am in.. I also wanna work on this issue.
Issue is to implement `prune_heads` as a method in `PretrainedModel`<|||||>@yugaljain1999 made some progress on this?<|||||>I think this is done. Happy to find new bugs if anyone is on the hunt!