Deprecate and Remove DynamoCommit

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

DynamoCommit was added to allow applications to be developed requiring conditional operations despite S3 being the only store not to natively support them. Since then AWS has added native support for conditional operations #54, we can therefore remove the DynamoCommit functionality.

Describe the solution you'd like

I would like to deprecate the DynamoCommit functionality and eventually remove it

Describe alternatives you've considered

Additional context

[crepererum]

Is this a candidate for #367 or do you wanna wait one full major release cycle?

[tustvold]

I think we can probably put it into #367