to prevent locking yourself out
test plan:
* have a multiple auth providers
* add a login to an admin explicitly tied to one of the providers
* log in with that login
* you should not be able to delete the auth provider tied to the
login you just used
Change-Id: I5d3a5e7ce0f33efee237e2b4764be50e72c792d9
Reviewed-on: https://gerrit.instructure.com/63259
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
Tested-by: Jenkins
QA-Review: August Thornton <august@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>