Remove string attribute from views

issue2350

view/relation_form.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. -->
-<form string="Relation" col="6">
+<form col="6">
     <label name="from_"/>
     <field name="from_"/>
     <label name="type"/>

view/relation_tree.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 string="Relations">
+<tree>
     <field name="from_"/>
     <field name="type"/>
     <field name="to"/>

view/relation_type_form.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. -->
-<form string="Party Relation Type">
+<form>
     <label name="name"/>
     <field name="name"/>
     <label name="reverse"/>

view/relation_type_tree.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 string="Party Relation Types">
+<tree>
     <field name="name"/>
     <field name="reverse"/>
 </tree>