ui_test: don't check planning box element position top

We could not find a portable way to use verifyElementPositionRangeTop.

See internal discussion `[test][erp5] update selenium test` for more
details.

bt5/erp5_ui_test/PathTemplateItem/portal_tests/planning_box_field_zuite/testPlanningBoxBlockPosition.zpt

@@ -138,21 +138,6 @@
   <td>id=group_3_activity_1_block_1</td>
   <td>552</td>
 </tr>
-<tr>
-  <td>verifyElementPositionRangeTop</td>
-  <td>id=group_1_activity_1_block_1</td>
-  <td>248..266</td>
-</tr>
-<tr>
-  <td>verifyElementPositionRangeTop</td>
-  <td>id=group_2_activity_1_block_1</td>
-  <td>328..346</td>
-</tr>
-<tr>
-  <td>verifyElementPositionRangeTop</td>
-  <td>id=group_3_activity_1_block_1</td>
-  <td>408..426</td>
-</tr>
 <tr>
   <td>verifyElementWidth</td>
   <td>id=group_1_activity_1_block_1</td>