Source: https://www.prestashop.com/forums/topic/337353-remove-view-gridlist-bottons/
Open themes/yourtheme/product-sort.tpl and find this code:
<ul class="display hidden-xs"> <li class="display-title">{l s='View:'}</li> <li id="grid"><a rel="nofollow" href="#" title="{l s='Grid'}"><i class="icon-th-large"></i>{l s='Grid'}</a></li> <li id="list"><a rel="nofollow" href="#" title="{l s='List'}"><i class="icon-th-list"></i>{l s='List'}</a></li> </ul>
Delete it and buttons will gone.