Make SVG size argument optional (#12814)

Now defaults to 16 on both frontend and backend.

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/js/markdown/anchors.js

@@ -23,7 +23,7 @@ export default function initMarkdownAnchors() {
     const a = document.createElement('a');
     a.classList.add('anchor');
     a.setAttribute('href', `#${encodeURIComponent(originalId)}`);
-    a.innerHTML = svg('octicon-link', 16);
+    a.innerHTML = svg('octicon-link');
     heading.prepend(a);
   }