Discussion: Remove sequential on master

Maybe we can collect some pros and cons for deleting the old sequential models on master?

Pros:

• Easier to maintain codebase (tests that need fixing, properties that have to be adapted)
• Less deprecation warnings (could be probably also suppressed)

Cons:

• If you want to use a sequential model you have to switch to Dumux releases/3.2 and Dune releases/2.7
• Depending on how long it takes to reimplement the models in the new model scheme the code and tests might be harder to reproduce