[FIX] point_of_sale: redundance in report.pos.order search view

Avoid double entry in search filters of POS reporting.
Replace by 2 other usefull filters.

Closes #4600

addons/point_of_sale/report/pos_order_report_view.xml

@@ -28,8 +28,8 @@
                     <filter string="My Sales" help="My Sales" domain="[('user_id','=',uid)]"/>
                     <field name="partner_id"/>
                     <field name="user_id"/>
-                    <field name="partner_id"/>
-                    <field name="user_id"/>
+                    <field name="product_id"/>
+                    <field name="product_categ_id"/>
                     <group expand="1" string="Group By">
                         <filter string="Salesperson" name="User" context="{'group_by':'user_id'}"/>
                         <filter string="Product Category" context="{'group_by':'product_categ_id'}"/>