Only set enableLinkTracking once for matomo

It complains otherwise:
"The method enableLinkTracking is registered more than once in "_paq" variable."

assets/vpu-signature.html.ejs

@@ -65,7 +65,6 @@
             _paq.push(['MediaAnalytics::scanForMedia', content]);
             _paq.push(['FormAnalytics::scanForForms', content]);
             _paq.push(['trackContentImpressionsWithinNode', content]);
-            _paq.push(['enableLinkTracking']);
         });
 
         // track errors