feat: replace get_act_fn for gpt_bigcode

[zhyncs]

Motivation

For gpt bigcode, it only uses gelu or gelu_pytorch_tanh.

The parts of distributed and quant will be completely removed later.

Modifications

Checklist

• Format your code according to the Contributor Guide.
• Add unit tests as outlined in the Contributor Guide.
• Update documentation as needed, including docstrings or example tutorials.