Actually, after talking to @dangoor I'm going to leave this cleanup to him -- some of the unit tests still call this function directly.

Seems ok to me to remove the tests if they're basically redundant with the node-side unit tests that test validation in isolation.  Otherwise, we could turn this into a unit-test-only underscore-prefixed method (feels a little iicky to me) or try to move it out of here & into the unit tests module (which I think would be a bit tricky due to the _nodeConnectionDeferred stuff).