Remove tutorials

[NiklasVin]

Main changes of this PR

Removes tutorials from the adapter repository.

Motivation and additional information

Before creating a first release of the adapter, the tutorials should be moved to the tutorials repository. Cf. precice/tutorials#688 and precice/tutorials#687

Author's checklist

• I updated the changelog file CHANGELOG.md if there are user-observable changes since the last release.
• I squashed / am about to squash all commits that should be seen as one.

Reviewers' checklist

• Does the changelog entry make sense? Is it formatted correctly?
• Do you understand the code changes?

[IshaanDesai]

Looks good 👍

[IshaanDesai]

An open question here is whether we still want to run the tutorial case in the CI, or if it would be better practice to add a system test for it. @MakisH what do you think?

[MakisH]

These are independent: you might still want to run a tutorial that only requires FEniCSx (or the upcoming preCICE mock), as a lightweight system test in your regular CI.

A system test should definitely be added.