rm run_name, add_seed_and_date_to_exp_name

[garrett361]

This PR proposes two changes to the SFT finetune.py script:

1. Remove the currently-unused run_name arg
2. Allow the user to avoid appending the seed and date to the exp_name

For the first point, run_name is never actually used in the script. Instead, it is immediately overwritten by the exp_name value:

open-instruct/open_instruct/finetune.py

Line 416 in 82632dd

args.run_name = f"{args.exp_name}__{args.seed}__{int(time.time())}"

So, I propose removing this no-op arg.

For the second point, it is not always desirable to add the seed and start time to the experiment name. Some reasons:

1. The date causes the experiment name to change when resuming an experiment.
2. In multi-node scenarios, the date can be different on each node and the date affects the name of the checkpoint directory, which I believe can cause issues with checkpointing and restart.

[garrett361]

Thanks, @hamishivi!