Bump loader-utils and webpack in /extension

Removes [loader-utils](https://github.com/webpack/loader-utils). It's no longer used after updating ancestor dependency [webpack](https://github.com/webpack/webpack). These dependencies need to be updated together.


Removes `loader-utils`

Updates `webpack` from 2.3.2 to 5.74.0
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](webpack/webpack@v2.3.2...v5.74.0)

---
updated-dependencies:
- dependency-name: loader-utils
  dependency-type: indirect
- dependency-name: webpack
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>