Allow U2F 2FA without TOTP (#11573)

This change enables the usage of U2F without being forced to enroll an TOTP authenticator.
The `/user/auth/u2f` has been changed to hide the "use TOTP instead" bar if TOTP is not enrolled.

Fixes #5410
Fixes #17495

templates/user/settings/security_twofa.tmpl

@@ -3,7 +3,7 @@
 </h4>
 <div class="ui attached segment">
 	<p>{{.i18n.Tr "settings.twofa_desc"}}</p>
-	{{if .TwofaEnrolled}}
+	{{if .TOTPEnrolled}}
 	<p>{{$.i18n.Tr "settings.twofa_is_enrolled" | Str2html }}</p>
 	<form class="ui form" action="{{AppSubUrl}}/user/settings/security/two_factor/regenerate_scratch" method="post" enctype="multipart/form-data">
 		{{.CsrfTokenHtml}}