Remove unneeded and update needed container for CI

In need to update Docker images build on Ubuntu 18.04 as this can give problems with the tests and I do not plan to support 18.04 anymore. Additionally, we are switiching to preCICE v2 which has been released about a year ago.

• dumux-precice:3.3git-iterative-pr-1.6.1 has been moved to nightly, but will most likely fail, see !10 (merged)
  • I am not sure whether I need any of the 3.3git-iterative-pr anymore.
• All images containing preCICE before 2.0.0 and using Ubuntu 18.04 need to be updated or remobed.

assigned to @ajaust

mentioned in merge request !10 (merged)

added maintenance label

Fixed by !12 (merged).

closed