[REM] Remove 'state' group_by filter in purchase order line search view (opw: 727796)

The group by on state in this search view cannot be used due to a typo
in the 'state' field's attribute "stored=True" dbe3d803

It can't be fixed in 9.0 as it would change the schema, hence the only
option is to disable this filter in 9.0

This should not to be forward ported to 10.0 as it is already fixed for
this version in 3451ac52

addons/purchase/purchase_view.xml

@@ -482,7 +482,10 @@
                         <filter name="groupby_supplier" string="Vendor" domain="[]" context="{'group_by' : 'partner_id'}" />
                         <filter name="groupby_product" string="Product" domain="[]" context="{'group_by' : 'product_id'}" />
                         <filter string="Order Reference" domain="[]" context="{'group_by' :'order_id'}"/>
-                        <filter string="Status" domain="[]" context="{'group_by' : 'state'}" />
+                        <!-- Commented out because of the 'state' field's attribute typo "stored=True"
+                             that can't be fixed in 9.0 as it would change the schema. Hence the only
+                             option is to disable this filter. Not to be forward ported to 10.0 !
+                        <filter string="Status" domain="[]" context="{'group_by' : 'state'}" /> -->
                     </group>
                 </search>
             </field>