Removed datetime_cast_sql, which is never overridden or used anywhere in Django.

Thanks Tim Graham for review.

django/db/backends/base/operations.py

@@ -90,15 +90,6 @@ class BaseDatabaseOperations(object):
         """
         raise NotImplementedError('subclasses of BaseDatabaseOperations may require a datetrunc_sql() method')
 
-    def datetime_cast_sql(self):
-        """
-        Returns the SQL necessary to cast a datetime value so that it will be
-        retrieved as a Python datetime object instead of a string.
-
-        This SQL should include a '%s' in place of the field's name.
-        """
-        return "%s"
-
     def datetime_cast_date_sql(self, field_name, tzname):
         """
         Returns the SQL necessary to cast a datetime value to date value.

docs/releases/1.9.txt

@@ -541,6 +541,12 @@ Database backend API
   :class:`~django.db.models.TimeField`, and may be needed by third-party
   database backends.
   
+* The ``DatabaseOperations.datetime_cast_sql()`` method (not to be confused
+  with ``DatabaseOperations.datetime_cast_date_sql()`` mentioned above)
+  has been removed. This method served to format dates on Oracle long
+  before 1.0, but hasn't been overridden by any core backend in years
+  and hasn't been called anywhere in Django's code or tests.
+
 Default settings that were tuples are now lists
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~