edit the file \fengoffice\application\views\access\login.php
remove line 33 - 36:
<div style="margin-top: 6px">
<?php echo checkbox_field('login[remember]', array_var($login_data, 'remember') == 'checked', array('id' => 'loginRememberMe')) ?>
<label class="checkbox" for="loginRememberMe"><?php echo lang('remember me') ?></label>
</div>