Remove unused css class

lms/static/sass/course/base/_base.scss

@@ -152,15 +152,6 @@ img {
     color: #fff;
   }
 
-  .error-icon {
-    display: block;
-    float: left;
-    width: 27px;
-    height: 24px;
-    margin: 0 auto 10px;
-    background: url(../images/large-error-icon.png) no-repeat;
-  }
-
   strong {
     display: block;
     margin-bottom: 10px;
@@ -192,4 +183,4 @@ img {
     margin-top: 10px;
     text-align: center;
   }
-}
\ No newline at end of file
+}