Remove expected attributes from delete session

[JDutil]

When using dynamodb sessions the delete options contain expected attributes:
https://github.com/aws/aws-sessionstore-dynamodb-ruby/blob/master/lib/aws/session_store/dynamo_db/locking/base.rb#L68
https://github.com/aws/aws-sessionstore-dynamodb-ruby/blob/master/lib/aws/session_store/dynamo_db/locking/base.rb#L146

These work fine when using the application, but cause our spec suite to fail as the delete operation could attempt to delete a session not in the database. With expected attributes set it raises an error if the expected attributes are not within the database rather than failing silently.

Is it necessary to keep expected attributes or could I submit a pull request to either remove them or make them optional?