SI-6120 Suppress extra warnings

This is a mere polish for the fix to allow multiple warnings.

Sensibility checks in refchecks were shown to be redundant.

This commit includes a mild refactor to reduce tabbage, and
uses a local var to flag that a warning has already been emitted.

It would be better to have the checks return true if warned,
to facilitate `nonSensically || unrelatedly`, etc., but that's
a lot of `else false`.

The check files that were updated with the redundant warnings
are reverted.
Merge pull request #3276 from som-snytt/issue/6120-spurious-check

SI-6120 Suppress extra warnings