remove unused css variable

Signed-off-by: Matt Wrock <matt@mattwrock.com>

Author: mwrock

components/builder-web/app/app.scss

@@ -215,7 +215,6 @@ main {
 }
 
 footer {
-  $menu-width: 224px;
   z-index: 100;
   bottom: 0;
   color: currentcolor;