[FIX] account: reset the move reference on bank statement

When removing a move previously linked to a bank statement, the move_name value
must be removed too.
This field is set when reconciling the entries.
When move_name is set, it is not possible to delete the bank statement line,
even if the refered move no longer exists.

opw-741205

addons/account/models/account_move.py

@@ -174,6 +174,11 @@ def unlink(self):
             #check the lock date + check if some entries are reconciled
             move.line_ids._update_check()
             move.line_ids.unlink()
+
+            # remove reference set at statement reconciliation
+            if move.statement_line_id.move_name:
+                move.statement_line_id.move_name = False
+
         return super(AccountMove, self).unlink()
 
     @api.multi