Remove sort on complex header

QuesnelJ

Given:

<

table class="wb-tables table"
data-wb-tables='{"iDisplayLength": 50,
"columnDefs": [{"targets": [0], "sortable": true, "aDataSort": [0, 1, 3], "searchable": false},
{"targets": [1], "sortable": false, "visible": false},
{"targets": [2], "sortable": false},
{"targets": [3], "sortable": false},
{"targets": [4], "sortable": false},
{"targets": [5], "sortable": true, "aDataSort": [5, 0, 1, 3]},
{"targets": [6], "sortable": false},
{"targets": [7], "sortable": false},
{"targets": [8], "sortable": false, "searchable": false}]}'>
<thead>
<tr>
<th rowspan="2" class="text-center">Cycle</th>
<th rowspan="2" class="text-center">Numerical day</th>
<th rowspan="2" class="text-center">Day</th>
<th colspan="2" class="text-center">Time</th>
<th rowspan="2" class="text-center">Employee</th>
<th colspan="2" class="text-center">Effective dates</th>
<th rowspan="2" class="text-center">Actions</th>
</tr>
<tr>
<th class="text-center">Start</th>
<th class="text-center">End</th>
<th class="text-center">Start</th>
<th class="text-center">End</th>
</tr>
</thead>

How do I remove the sorting arrows on the "time" and "Effective dates" group headings?