accounting: only allow Assignor to restart accounting periods

This partially reverts 8a336dc5 (erp5_accounting: Allow
Assignor manage Accounting Periods, 2024-09-16) for the restart
transition, it is intentional that only Assignor can restart
an accounting period that have been closed.
The idea was to support a scenario where re-opening a period
that was closed can not be done directly by the Assignee but
needs validation from the assignor.

bt5/erp5_accounting/WorkflowTemplateItem/portal_workflow/accounting_period_workflow/transition_restart_action.xml

@@ -44,7 +44,6 @@
             <value>
               <tuple>
                 <string>Assignor</string>
-                <string>Assignee</string>
               </tuple>
             </value>
         </item>