MNT Remove webauthn module from behat tests

[emteknetnz]

Issue silverstripe/.github#342

[GuySartorelli]

Oh! That's a side-effect I hadn't considered.

We should probably add a dummy verification method into frameworktest so we can keep the "select a verification method" part in the behat test.

It would not be ideal if that functionality stopped working, since we should still allow multiple verification methods to be available even if only one of them is in a supported module.

[emteknetnz]

If that's the case I think we should just keep webauthn as the "dummy verificaiton method"

Even though it's unsupported, the CMS 6 branch will still be around, so it can stay in require-dev

If you agree, just close this PR

[GuySartorelli]

Sounds fine to me - it's a require-dev so that won't affect projects.
If it causes us problems in the future we can revisit the decision.