[WIP] Deleting mpsGeneric

[parsonsmatt]

Fixes #1204

As expected, deleting from the library is a big simplification, but it is going to cause some issues with the test suites.

---

Before submitting your PR, check that you've:

• Documented new APIs with Haddock markup
• Added @since declarations to the Haddock
• Ran stylish-haskell on any changed files.
• Adhered to the code style (see the .editorconfig file for details)

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Bumped the version number if there isn't an (unreleased) on the Changelog
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)