To get rid of this button, open one of these files (which one - depends on what template you're using):

/components/com_virtuemart/themes/default/templates/browse/includes/browse_layouttable.tpl.php
/components/com_virtuemart/themes/default/templates/browse/includes/browse_listtable.tpl.php
/components/com_virtuemart/themes/default/templates/browse/includes/browse_notables.tpl.php

And comment line:

<?php //echo $parameter_form // The Parameter search form ?>