Remove string from tree and form tags.

view/sale_rule_action_form.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of sale_rule module for Tryton.
 The COPYRIGHT file at the top level of this repository contains the full
 copyright notices and license terms. -->
-<form string="Sale Rule" col="6">
+<form col="6">
     <label name="action_type"/>
     <field name="action_type"/>
     <label name="product"/>
@@ -13,4 +13,4 @@ copyright notices and license terms. -->
     <field name="rule"/>
     <separator name="comment" colspan="6"/>
     <field name="comment" colspan="6"/>
-</form>
+</form>

view/sale_rule_action_tree.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of the sale_rule module for Tryton.
 The COPYRIGHT file at the top level of this repository contains the full
 copyright notices and license terms. -->
-<tree string="Actions" sequence="sequence" editable="bottom">
+<tree sequence="sequence" editable="bottom">
     <field name="sequence"/>
     <field name="action_type"/>
     <field name="product"/>

view/sale_rule_condition_form.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of sale_rule module for Tryton.
 The COPYRIGHT file at the top level of this repository contains the full
 copyright notices and license terms. -->
-<form string="Sale Rule" col="8">
+<form col="8">
     <label name="criteria"/>
     <field name="criteria"/>
     <group colspan="2" col="4" id="product">
@@ -19,4 +19,4 @@ copyright notices and license terms. -->
     <field name="stop_further"/>
     <label name="rule"/>
     <field name="rule"/>
-</form>
+</form>

view/sale_rule_condition_tree.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of the sale_rule module for Tryton.
 The COPYRIGHT file at the top level of this repository contains the full
 copyright notices and license terms. -->
-<tree string="Conditions" sequence="sequence" editable="bottom">
+<tree sequence="sequence" editable="bottom">
     <field name="sequence"/>
     <field name="criteria"/>
     <field name="product"/>

view/sale_rule_form.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of sale_rule module for Tryton.
 The COPYRIGHT file at the top level of this repository contains the full
 copyright notices and license terms. -->
-<form string="Sale Rule" col="4">
+<form col="4">
     <label name="name"/>
     <field name="name"/>
     <group colspan="2" col="4" id="booleans">
@@ -35,4 +35,4 @@ copyright notices and license terms. -->
             <field name="actions" colspan="4"/>
         </page>
     </notebook>
-</form>
+</form>

view/sale_rule_tree.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of the sale_rule module for Tryton.
 The COPYRIGHT file at the top level of this repository contains the full
 copyright notices and license terms. -->
-<tree string="Sale Rules" sequence="sequence">
+<tree sequence="sequence">
     <field name="sequence"/>
     <field name="name"/>
     <field name="from_date" widget="date"/>