[FIX] product,purchase,point_of_sale: force empty values for dropped fields

At 96f038a product-related fields were removed due
to an important product.template/product.product
refactoring. As the field values were simply
dropped, they may not be nullified when upgrading an
existing database. Forcing them to False will take
care of it.

addons/point_of_sale/point_of_sale_view.xml

@@ -169,6 +169,8 @@
             <field name="view_mode">tree,form,kanban</field>
             <field name="context" eval="{}"/>
             <field name="domain" eval="[('available_in_pos','&lt;&gt;',False)]"/>
+            <field name="search_view_id" eval="False"/> <!-- Force empty -->
+            <field name="view_id" eval="False"/> <!-- Force empty -->
             <field name="help" type="html">
               <p class="oe_view_nocontent_create">
                 Click to add a new product.

addons/product/product_view.xml

@@ -195,6 +195,7 @@
             <field name="view_mode">tree,form,kanban</field>
             <field name="view_type">form</field>
             <field name="search_view_id" ref="product_search_form_view"/>
+            <field name="view_id" eval="False"/> <!-- Force empty -->
             <field name="help" type="html">
               <p class="oe_view_nocontent_create">
                 Click to define a new product.

addons/purchase/purchase_view.xml

@@ -125,6 +125,8 @@
         <field name="view_type">form</field>
         <field name="view_mode">kanban,tree,form</field>
         <field name="context">{"search_default_filter_to_purchase":1}</field>
+        <field name="search_view_id" eval="False"/> <!-- Force empty -->
+        <field name="view_id" eval="False"/> <!-- Force empty -->
         <field name="help" type="html">
           <p class="oe_view_nocontent_create">
             Click to define a new product.