'Remove a refname only if it currently equals old_ref.
This method does not follow symbolic references, even if applicable for
the subclass. It can be used to perform an atomic compare-and-delete
operation.
:param name: The refname to delete.
:param old_ref: The old sha the refname must refer to, or None to
delete unconditionally.
:return: True if the delete was successful, False otherwise.'

def remove_if_equals(self, name, old_ref):

    raise NotImplementedError(self.remove_if_equals)
