[functorch] Update notebooks for latest release (#85855)
This PR:
- dedups our colab notebooks with the regular functorch notebooks. The
colab notebooks were versions of the reuglar notebooks that had
install instructions. Now that functorch is easier to install, we do not
need those anymore.
- fixes the colab links
Test Plan:
- build docs locally and tested them
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85855
Approved by: https://github.com/samdow
