Remove nonexistent sequence from purchase request quotation line view

Closes #13541
(grafted from 21ee3ac23dfc9b162d3d2deb5c98a1b9dafdd069)

--HG--
branch : 7.0

modules/purchase_request_quotation/view/purchase_request_quotation_line_list_request.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
-<tree sequence="sequence">
+<tree>
     <field name="quotation" expand="1"/>
     <field name="supply_date" optional="0"/>
     <field name="supplier" expand="1" optional="0"/>