Do not show mobile column actions for Link column

Refs #2669

datasette/static/mobile-column-actions.js

@@ -5,7 +5,9 @@ var MOBILE_COLUMN_DIALOG_TITLE_ID = "mobile-column-actions-title";
 function mobileColumnHeaders(manager) {
   return Array.from(
     document.querySelectorAll(manager.selectors.tableHeaders),
-  ).filter((th) => th.dataset.column);
+  ).filter(
+    (th) => th.dataset.column && th.querySelector(".dropdown-menu-icon"),
+  );
 }
 
 function mobileColumnMetaText(th) {