unstructured

c9976760 - fix: revert back to old requirements file for sphinx docs (#3077)

fix: revert back to old requirements file for sphinx docs (#3077) ### Summary As seen in [this job](https://github.com/Unstructured-IO/unstructured/actions/runs/9182534479/job/25251583102), the build job for sphinx docs is failing, and has been failing for quite some time. This PR reverts the requirements file back to a [previous good commit](https://github.com/Unstructured-IO/unstructured/commit/91b892c79deadb5356abd83609d68529bbc1edee) for that job, and also moves the `build.in` file so the requirements file doesn't get update on `make pip-compile.` This is fine since those requirements don't get installed as part of the package, and we're deprecated the `sphinx` docs in favor of https://docs.unstructured.io anyway. ### Testing Build was [successful](https://github.com/Unstructured-IO/unstructured/actions/runs/9198605026/job/25301670934?pr=3077) on the feature branch. --------- Co-authored-by: Christine Straub <christinemstraub@gmail.com>