How to disable the keyword field in the search results? 

In the following picture you can see the search Results Screen, in this screen you can see in the bottom the legend "Search Our Catalog" in Yellow. 

To disable it, go to the Cart Setup in the Shopping cart Administration Tools and you will find these fields in the bottom. Just leave the "Search by keyword Title" in blank and the field will not appear in the search results screen again.
 

This help is valid only if you have disable the Custom header and Footer