Revert "Add global "locale" config option"

This reverts commit 9e90c77, because it caused a bug that affected
different people just after being released:
https://github.com/adrienverge/yamllint/issues/285
https://github.com/adrienverge/yamllint/issues/286

docs/configuration.rst

@@ -189,22 +189,3 @@ Here is a more complex example:
      ignore: |
        *.ignore-trailing-spaces.yaml
        ascii-art/*
-
-Setting the locale
-------------------
-
-It is possible to set the ``locale`` option globally. This is passed to Python's
-`locale.setlocale
-<https://docs.python.org/3/library/locale.html#locale.setlocale>`_,
-so an empty string ``""`` will use the system default locale, while e.g.
-``"en_US.UTF-8"`` will use that. If unset, the default is ``"C.UTF-8"``.
-
-Currently this only affects the ``key-ordering`` rule. The default will order
-by Unicode code point number, while other locales will sort case and accents
-properly as well.
-
-.. code-block:: yaml
-
- extends: default
-
- locale: en_US.UTF-8