The compare to empty string checker (``pylint.extensions.emptystring``) and the compare to
zero checker (``pylint.extensions.compare-to-zero``) have been removed and their checks are
now part of the implicit booleaness checker:

``compare-to-zero`` was renamed ``use-implicit-booleaness-not-comparison-to-zero`` and
``compare-to-empty-string`` was renamed ``use-implicit-booleaness-not-comparison-to-string``
and they now need to be enabled explicitly.

The `pylint.extensions.emptystring`` and ``pylint.extensions.compare-to-zero`` extensions
no longer exists and needs to be removed from the ``load-plugins`` option.

This permits to make their likeness explicit and will provide better performance as they share most of their
conditions to be raised.

Refs #6871