Make deposit optional on party list

Like the receivable and payable today fields.

modules/account_deposit/view/party_tree.xml

@@ -2,9 +2,7 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <data>
-    <xpath
-        expr="/tree/field[@name='payable_today']"
-        position="after">
-        <field name="deposit"/>
+    <xpath expr="/tree/field[@name='payable_today']" position="after">
+        <field name="deposit" optional="0"/>
     </xpath>
 </data>