Remove string attribute from views

issue2350

view/currency_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="Currency" col="6">
+<form col="6">
     <label name="name"/>
     <field name="name"/>
     <label name="symbol"/>

view/currency_rate_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="Rate">
+<form>
     <label name="currency"/>
     <field name="currency"/>
     <newline/>

view/currency_rate_graph.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. -->
-<graph string="Rates" type="line">
+<graph type="line">
     <x>
         <field name="date"/>
     </x>

view/currency_rate_list.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="Rates">
+<tree>
     <field name="currency"/>
     <field name="date"/>
     <field name="rate"/>

view/currency_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="Currencies">
+<tree>
     <field name="name"/>
     <field name="symbol"/>
     <field name="code"/>