Improve admin/labels page ui

Remove unnecessary gray block around no labels message.
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/admin/labels/destroy.js.haml

-- if @labels.size == 0
-  $('.labels').load(document.URL + ' .card.bg-light').hide().fadeIn(1000)
+- if @labels.size.zero?
+  $('.labels').load(document.URL + ' .nothing-here-block').hide().fadeIn(1000)

app/views/admin/labels/index.html.haml

@@ -14,6 +14,4 @@
 
     = paginate @labels, theme: 'gitlab'
   - else
-    .card.bg-light
-      .nothing-here-block= _('There are no labels yet')
-
+    .nothing-here-block= _('There are no labels yet')