Revert "Error (also in original) model, scaling only q matrix not qk.T dot product (qk.T/sqrt(dim_per_head))"
Reverts huggingface/transformers#21627

This PR changed the modeling code and as a result broke training as reported in #22426 
Moreover, since the "error" was in the original code from the authors, it's not an error anymore but a feature.

This will be put in the patch v4.27.4
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_22444). All of your documentation changes will be reflected on that endpoint.