[train] Simplify `test_transformers_trainer_steps::test_e2e_steps`

[matthewdeng]

#35270 causes importing ray.train.huggingface to import accelerate, which takes approximately 4.5 seconds. Since this test is parameterized to run 20x times, this causes the total time to run this test to increase the threshold from large to enormous.

To reduce the time for this test, we can take a few approaches:

1. Reduce the general runtime of the test by plugging in a dummy model.
2. Reduce the number of configurations we are testing.
3. Move the import of accelerate to be further lazy and only import when it is actually needed.

[cszhu]

This P2 issue has seen no activity in the past 2 years. It will be closed in 2 weeks as part of ongoing cleanup efforts.

Please comment and remove the pending-cleanup label if you believe this issue should remain open.

Thanks for contributing to Ray!