Hide OTP prompt on /adminon when irrelevant.

If the user doesn't have an OTP secret and an OTP isn't required for
turning on admin mode, we'll just hide the prompt to avoid confusion.

r2/r2/templates/passwordverificationform.html

@@ -43,6 +43,7 @@
       ${error_field("WRONG_PASSWORD", "password")}
       </%utils:round_field>
 
+      % if not g.disable_require_admin_otp or c.user.otp_secret:
       <%utils:round_field title="${_('one-time password')}" description="${_('(required)')}" css_class="adminpasswordform">
       <input type="text" name="otp" maxlength="6" tabindex="1" required pattern="[0-9]{6}" autocomplete="off"
       % if c.otp_cached:
@@ -61,6 +62,7 @@
           % endif
           > ${_("remember this computer")}</label>
       </%utils:round_field>
+      % endif
 
       <p><button type="submit" class="btn" tabindex="1">${_('turn admin on')}</button></p>
       <p class="status error"></p>