ui: 移除题目导出中的lastModified标记

packages/ui-default/templates/problem_import.html

@@ -8,7 +8,7 @@
           <input type="hidden" name="csrfToken" value="{{ handler.csrfToken }}">
           <p>{{ _('Upload zipfile') }} {% if type %}({{ _('Type') }}: {{type}}){% endif %}:
             <input type="file" name="file">
-            {% if handler.user.hasPriv(PRIV.PRIV_EDIT_SYSTEM) not type %}<input type="checkbox" name="keepUser">{% endif %}
+            {% if handler.user.hasPriv(PRIV.PRIV_EDIT_SYSTEM) and not type %}<input type="checkbox" name="keepUser">{% endif %}
             <input type="submit" value="{{ _('Upload') }}" class="rounded primary button">
           </p>
         </form>