'Removes a source identifier from an existing RDS event
notification subscription.
:type subscription_name: string
:param subscription_name: The name of the RDS event notification
subscription you want to remove a source identifier from.
:type source_identifier: string
:param source_identifier: The source identifier to be removed from the
subscription, such as the **DB instance identifier** for a DB
instance or the name of a security group.'

def remove_source_identifier_from_subscription(self, subscription_name, source_identifier):

    params = {'SubscriptionName': subscription_name, 'SourceIdentifier': source_identifier}
    return self._make_request(action='RemoveSourceIdentifierFromSubscription', verb='POST', path='/', params=params)
