Issue #2358683 by MarkoT91 | LewisNyman: Move forum icons into the forum module.

core/modules/forum/css/forum.module.css

@@ -16,7 +16,7 @@
   white-space: nowrap;
 }
 #forum .icon{
-  background-image: url(../../../misc/forum-icons.png);
+  background-image: url(../icons/forum-icons.png);
   background-repeat: no-repeat;
   float: left; /* LTR */
   height: 24px;