[FIX] account: auto-balance opening entry

If the opening entry is balanced, the auto-balance line is unlinked.
However, before unlinking we test if it is balanced, which it is not. A
solution is removing the line from the move and it will be unlinked
automatically.

closes odoo/odoo#42930

Signed-off-by: oco-odoo <oco-odoo@users.noreply.github.com>

addons/account/models/company.py

@@ -390,7 +390,7 @@ class ResCompany(models.Model):
             if float_is_zero(debit_diff + credit_diff, precision_rounding=currency.rounding):
                 if balancing_move_line:
                     # zero difference and existing line : delete the line
-                    balancing_move_line.unlink()
+                    self.account_opening_move_id.line_ids -= balancing_move_line
             else:
                 if balancing_move_line:
                     # Non-zero difference and existing line : edit the line