Use context var rather than removed method

The method was removed here:
8be977883a16afd8

But the template code which used it was added in a separate PR here:
88eb7d5537a4b49d

So while each PR's tests passed, their merge didn't.

airlock/templates/file_browser/index.html

@@ -113,7 +113,7 @@
           {% if release_request.status.name %}
             data-request-status="{{ release_request.status.name }}"
           {% endif %}
-          {% if release_request.all_files_reviewed %}
+          {% if user_has_reviewed_all_files %}
             data-all-files-reviewed="true"
           {% endif %}
           {% if release_request.all_files_approved %}