Remove deprecated order_by docs

docs/ref/filterset.txt

@@ -10,7 +10,6 @@ Meta options
 - :ref:`model <model>`
 - :ref:`fields <fields>`
 - :ref:`exclude <exclude>`
-- :ref:`order_by <order-by>`
 - :ref:`form <form>`
 - :ref:`together <together>`
 - filter_overrides
@@ -92,40 +91,6 @@ declared directly  on the ``FilterSet``.
             exclude = ['password']
 
 
-.. _order-by:
-
-Ordering using ``order_by``
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-You can allow the user to control ordering by providing the
-``order_by`` argument in the Filter's Meta class.  ``order_by`` can be either a
-``list`` or ``tuple`` of field names, in which case those are the options, or
-it can be a ``bool`` which, if True, indicates that all fields that
-the user can filter on can also be sorted on. An example of ordering using a list::
-
-    import django_filters
-
-    class ProductFilter(django_filters.FilterSet):
-        price = django_filters.NumberFilter(lookup_expr='lt')
-        class Meta:
-            model = Product
-            fields = ['price', 'release_date']
-            order_by = ['price']
-
-If you want to control the display of items in ``order_by``, you can set it to
-a list or tuple of 2-tuples in the format ``(field_name, display_name)``.
-This lets you override the displayed names for your ordering fields::
-
-    order_by = (
-        ('name', 'Company Name'),
-        ('average_rating', 'Stars'),
-    )
-
-Note that the default query parameter name used for ordering is ``o``.  You
-can override this by setting an ``order_by_field`` attribute on the
-``FilterSet``'s Meta class to the string value you would like to use.
-
-
 .. _form:
 
 Custom Forms using ``form``
@@ -202,29 +167,3 @@ filters for a model field, you can override ``filter_for_lookup()``. Ex::
 
             # use default behavior otherwise
             return super(ProductFilter, cls).filter_for_lookup(f, lookup_type)
-
-
-``get_ordering_field()``
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-If you want to use a custom widget, or in any other way override the ordering
-field you can override the ``get_ordering_field()`` method on a ``FilterSet``.
-This method just needs to return a Form Field.
-
-Ordering on multiple fields, or other complex orderings can be achieved by
-overriding the ``FilterSet.get_order_by()`` method. This is passed the selected
-``order_by`` value, and is expected to return an iterable of values to pass to
-``QuerySet.order_by``. For example, to sort a ``User`` table by last name, then
-first name::
-
-    class UserFilter(django_filters.FilterSet):
-        class Meta:
-            order_by = (
-                ('username', 'Username'),
-                ('last_name', 'Last Name')
-            )
-
-        def get_order_by(self, order_value):
-            if order_value == 'last_name':
-                return ['last_name', 'first_name']
-            return super(UserFilter, self).get_order_by(order_value)