GUAC-932: Replace green spinner with spinning cog.

guacamole/src/main/webapp/app/index/styles/ui.css

@@ -423,14 +423,3 @@ div.logout-panel {
 .button.back {
     background-image: url('images/action-icons/guac-back.png');
 }
-
-.loading {
-    background-image: url(images/spinner.gif);
-    background-position: center;
-    background-repeat: no-repeat;
-    min-height: 200px;
-}
-
-.loading * {
-    visibility: hidden;
-}