Drop useless ConstraintInsertionTC
This test does nothing and is here from the begining of repo history.
Now it raise an error "TypeError: Skipped expected string as 'msg' parameter, got 'SkipTest' instead. Perhaps you meant to use a mark?"
Just drop it.
Backed out changeset 741dc2590f90
It was for cube s3storage, but this piece of information was
apparently not in the email (used for review), so this patch was
published in the wrong repository. :-/