Please set the filter type to 'label', the filter editor will not display.
dg.datagrid('enableFilter', [{
field:'itemid',
type:'label'
},{
field:'listprice',
type:'numberbox',
options:{precision:1},
op:['equal','notequal','less','greater']
},{
field:'unitcost',
type:'numberbox',
options:{precision:1},
op:['equal','notequal','less','greater']
}]);