* The inputProject reference is no longer needed as we have model
  snapshots that freeze the import state. Originally, this reference
  was intended to host a copy of the imported FileProject state at the
  time of importing.
* The File Project can simply be accessed by ascending the containment
  hierarchy.
* The referenced caused model corruption when exporting a found
  solution from the DSE: The FileProject id was reset to some id > 0
  that is a duplicate of some random model element. Loading such a model
  violated basic assumptions and ambiguous references.

Issue-Ref: 3742
Issue-Url: https://af3-developer.fortiss.org/issues/3742


Signed-off-by: Alexander Diewald <diewald@fortiss.org>