About session_bookmark

[cirotix]

Hi @lambtron
I am working on the streams in order to make them incremental where it is possible and I'll make a PR with that. I have a question about the methods session_bookmarks
https://github.com/singer-io/tap-chargify/blob/master/tap_chargify/streams.py#L51-L61

I don't understand what they stand for. I do not find any reference to them in the tap-chargify module, and I do not find any reference neither in Singer code (I am quite new to Singer so I don't know if this is an API method).

If this is dead code do you think that I can remove it?