FEniCSx as a participant is no longer maintained

[IshaanDesai]

In #488, FEniCSx as a participant in the partitioned-heat-conduction was moved from the develop branch to the fenicsx-cases branch. This branch is intended to be used to store FEniCSx participants as they are not currently part of the distribution release cycle. This is elaborated further in #467.

[MakisH]

I understand that there is nothing to act on regarding this issue at the moment. Let's close it and reopen it when FEniCSx becomes relevant again.

[BenjaminRodenberg]

Update on this issue: @NiklasVin is currently working on reviving our FEniCS-X adapter + tutorials.

[BenjaminRodenberg]

I think it makes more sense at the moment to continue developing the case directly in https://github.com/precice/fenicsx-adapter/. This simplifies the development at the current state and also makes the case more visible. We can move it to the tutorials when things are working again. Let's still keep this PR here open as a reminder.