Revert #634 and update reference results

[MakisH]

After releasing preCICE v3.2.0, we should update the reference results for the system tests and revert the changes introduced by #634. Besides the performance improvements we are missing, the configuration parameter <preconditioner update-on-threshold="<bool>" /> is not available pre-v3.2.0.

Checklist:

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md. -> Removed the one from Enforce recomputation of preconditioner to avoid regression #634.
• Update the reference results in the same PR.

[uekerman]

If we touch this, I would suggest to directly switch to the default everywhere, e.g.

<acceleration:IQN-ILS>
  <data name="Displacement" mesh="Solid-Mesh" />
  <data name="Force" mesh="Solid-Mesh" />
</acceleration:IQN-ILS>