override unlink methods to fix cascade delete fiscal_year>periods>date_ranges

--HG-- branch : 16.0

doc/index.rst

+.. |coverage| image:: .badges/coverage.svg
+    :target: https://orus.io/xcg/odoo-modules/account_period/-/pipelines?ref=branch/16.0
+    :alt: Coverage report
+.. |pylint| image:: .badges/pylint.svg
+    :target: https://orus.io/xcg/odoo-modules/account_period/-/pipelines?ref=branch/16.0
+    :alt: pylint score
+
+|coverage| |pylint|
+
 .. include:: README.rst
 
 Contents:
@@ -15,4 +24,3 @@
 * :ref:`genindex`
 * :ref:`modindex`
 * :ref:`search`
-