Corrected naming of method and attribute

* A :ref:`generic mechanism to handle the deprecation of model fields

  <migrations-removing-model-fields>` was added.

* The :attr:`RunPython.noop <django.db.migrations.operations.RunPython.noop>`

  and :meth:`RunSQL.noop() <django.db.migrations.operations.RunSQL.noop>` class

  attribute/method were added to ease in making ``RunPython`` and ``RunSQL``

* The :meth:`RunPython.noop() <django.db.migrations.operations.RunPython.noop>`

  and :attr:`RunSQL.noop <django.db.migrations.operations.RunSQL.noop>` class

  method/attribute were added to ease in making ``RunPython`` and ``RunSQL``

  operations reversible.

* The :class:`~django.db.migrations.operations.RunPython` and