You can go to file: /components/com_community/templates/jomsocial/layouts/people.browse.php
Comment or remove this snippet of code:
<?php if (isset($hasMultiprofile) && $hasMultiprofile && !isset($isAdvanceSearch) && count($multiprofileArr)> 0): ?>
<select class="joms-select" onchange="window.location=this.value;">
<?php foreach ($multiprofileArr as $key => $value) { ?>
<option value="<?php echo $value['url']; ?>" <?php if ($value['selected']) echo 'selected="selected"'; ?>>
<?php echo $value['name']; ?>
</option>
<?php } ?>
</select>
<?php endif; ?>