Wipe U2F keys too when disabling 2FA

actions.go

@@ -320,6 +320,14 @@ func (s *AccountService) disable2FA(ctx context.Context, tx TX, user *User) erro
 		return newBackendError(err)
 	}
 
+	// Disable U2F.
+	if len(user.U2FRegistrations) > 0 {
+		user.U2FRegistrations = nil
+		if err := tx.UpdateUser(ctx, user); err != nil {
+			return newBackendError(err)
+		}
+	}
+
 	// Wipe all app-specific passwords.
 	for _, asp := range user.AppSpecificPasswords {
 		if err := tx.DeleteApplicationSpecificPassword(ctx, user, asp.ID); err != nil {