modified oldestRevision from the 2nd FB

packages/app/src/components/PageHistory/PageRevisionTable.jsx

@@ -124,8 +124,7 @@ class PageRevisionTable extends React.Component {
         previousRevision = revision; // if it is the first revision, show full text as diff text
       }
 
-      let isOldestRevision = false;
-      if (revision === oldestRevision) isOldestRevision = true;
+      const isOldestRevision = revision === oldestRevision;
 
       const hasDiff = revision.hasDiffToPrev !== false; // set 'true' if undefined for backward compatibility