remove blazy integration

[chrfritsch]

Make sure these boxes are checked before submitting your pull request - thank you!

• [ ] All coding styles are fulfilled. (How to check for cs issues?)
• [ ] All tests are running locally. (How to run the test?)
• [ ] Necessary update hooks are provided.
• [ ] User roles have correct access for new introduced permission.
• [ ] Every thunder module has a README.md in its root. Follow this guidelines, but we don't need every topic.
• [ ] Code is covered with well-balanced amount of inline comments.
• [ ] New features or changes are documented.

If you are really awesome, then your feature is covered by additional tests. Well done!

[chrfritsch]

@dbosen and I disscussed this and we concluded to:

• Postpone the PR until the core patch for responsive image styles is released (hopefully 9.4)
• Change default config in 6.4 then
• Create a drush command to switch to the core implementation
• Leave slick and blazy dependencies until morpho