Bump postcss and parcel

Bumps [postcss](https://github.com/postcss/postcss) and [parcel](https://github.com/parcel-bundler/parcel). These dependencies needed to be updated together.

Removes `postcss`

Updates `parcel` from 1.12.4 to 2.7.0
- [Release notes](https://github.com/parcel-bundler/parcel/releases)
- [Changelog](https://github.com/parcel-bundler/parcel/blob/v2/CHANGELOG.md)
- [Commits](https://github.com/parcel-bundler/parcel/compare/[email protected])

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: parcel
  dependency-type: direct:development
...

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