remove unused CSS var

Author: slorber

website/src/css/customTheme.scss

@@ -43,7 +43,6 @@
   --ifm-table-border-color: var(--ifm-toc-border-color);
   --ifm-table-cell-padding: 10px;
   --ifm-table-stripe-background: rgba(0, 0, 0, 0.02);
-  --docusaurus-blog-social-icon-size: 16px;
 
   @media (min-width: 340px) {
     --ifm-navbar-sidebar-width: 340px;