Remove behat only entry page fixtures

Behat is being used for the wrong thing. We have in core entry pages only available to behat in order to test low level form elements and other rubbish.

This is not the purpose of behat and having these tests in core encourages devs to copy this model in future. These entry pages expose unnecessary risks to production sites. Behat tests should use real pages or not at all.

See lib/form/tests/fixtures - they all must go.