Bump tough-cookie and node-sass in /slides

Removes [tough-cookie](https://github.com/salesforce/tough-cookie). It's no longer used after updating ancestor dependency [node-sass](https://github.com/sass/node-sass). These dependencies need to be updated together.


Removes `tough-cookie`

Updates `node-sass` from 7.0.3 to 9.0.0
- [Release notes](https://github.com/sass/node-sass/releases)
- [Changelog](https://github.com/sass/node-sass/blob/master/CHANGELOG.md)
- [Commits](sass/node-sass@v7.0.3...v9.0.0)

---
updated-dependencies:
- dependency-name: tough-cookie
  dependency-type: indirect
- dependency-name: node-sass
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]