Fix items table potentially not rendering after merge

In d4f8c7c an entry has been removed from zotero.properties that is still being
used in items table. If `numNotes` column is visible, items table would not
render.

Instead of re-adding to zotero.properties, I've migrated this string to
zotero.ftl to fix this problem.

chrome/content/zotero/itemTree.jsx

@@ -2814,7 +2814,8 @@ var ItemTree = class ItemTree extends LibraryTree {
 		else {
 			cell = renderCell.apply(this, arguments);
 			if (column.dataKey === 'numNotes' && data) {
-				cell.setAttribute('aria-label', Zotero.getString('pane.item.notes.count', data, data) + '.');
+				cell.dataset.l10nId = 'items-table-cell-notes';
+				cell.dataset.l10nArgs = JSON.stringify({ count: data });
 			}
 			else if (column.dataKey === 'itemType') {
 				cell.setAttribute('aria-hidden', true);

chrome/locale/en-US/zotero/zotero.ftl

@@ -87,6 +87,12 @@ import-online-relink-only =
     .label = Relink Mendeley Desktop citations
 import-online-relink-kb = More Information
 
+items-table-cell-notes =
+    .aria-label = { $count ->
+        [one] { $count } Note
+        *[other] { $count } Notes
+    }
+
 report-error =
     .label = Report Error…