...
<layout class="QGridLayout" name="page_4">
 <item row="0" column="0">
  <!-- below is the layout you want to remove -->
  <layout class="QVBoxLayout" name="verticalLayout_1">
   <item>
    <layout class="QGridLayout" name="gridLayout_8">
      ...
    </layout>
   </item>
  </layout>
 </item>
</layout>
...

...
<layout class="QGridLayout" name="page_4">
 <item row="0" column="0">
  <layout class="QGridLayout" name="gridLayout_8">
      ...
  </layout>
 </item>
</layout>
...