[FIX] website_mail: remove unused alert div, fixes look of input-group-btn

Bootstrap's CSS depends on the input-group-btn
element being the first/last child of its parent.
This was not the case because of the invisible
and useless alert.

addons/website_mail/static/src/js/follow.js

@@ -19,9 +19,8 @@
                 self.$target.removeClass("hidden");
             });
 
-            // not if editable mode to allow designer to edit alert field
+            // not if editable mode to allow designer to edit
             if (!editable_mode) {
-                $('.js_follow > .alert').addClass("hidden");
                 $('.js_follow > .input-group-btn.hidden').removeClass("hidden");
                 this.$target.find('.js_follow_btn, .js_unfollow_btn').on('click', function (event) {
                     event.preventDefault();

addons/website_mail/views/website_mail.xml

@@ -16,7 +16,6 @@
             <button href="#" t-attf-class="btn btn-default js_unfollow_btn">Unsubscribe</button>
             <button href="#" t-attf-class="btn btn-primary js_follow_btn">Subscribe</button>
         </span>
-        <div class="alert alert-success hidden">Thanks for your subscription!</div>
     </div>
 </template>