Constraints: Fixup decompose mechanism for constrained model elements

• In the decompose mechanism, the constrained instances are duplicated since the resolution of #3293. It is sufficient to remove the contrained instances from the container by clearing the list since the hierarchical decomposition takes care of the destruction of contained specifications.
• Tests: Deleting a component with a test suite succeeds, deleting test suites and test suite specs succeeds. The "All tests pass" constraint seems to work: It is marked green in a one-component system with a "successful" test suite (NOTE: there are currently focus problems, so one might need to click into the navigator).

Issue-Ref: 3523 Issue-Url: https://af3-developer.fortiss.org/issues/3523Signed-off-by: Alexander Diewald's avatarAlexander Diewald diewald@fortiss.org