Remove unused set_tax_code import in scenario

tests/scenario_invoice_correction.rst

@@ -10,7 +10,7 @@ Imports::
     >>> from trytond.modules.company.tests.tools import create_company, \
     ...     get_company
     >>> from trytond.modules.account.tests.tools import create_fiscalyear, \
-    ...     create_chart, get_accounts, create_tax, set_tax_code
+    ...     create_chart, get_accounts, create_tax
     >>> from trytond.modules.account_invoice.tests.tools import \
     ...     set_fiscalyear_invoice_sequences