please remove permission check that disallows private-group access.

[Damien Miller]

On Mon, 22 Oct 2018, Charlie Smurthwaite wrote:

> Generally, giving users the choice should not be controversial, but I will
> note that there is the mild fear of a user googling the error and finding
> misguided advice to simply disable the check.

That's exactly what I believe will happen if we include an option.
Then we're stuck having to maintain a useless option in perpetuity.