We removed that some time ago because way too many people were screwing up the process and it was too complicated for them. (it also wasn't the documented way to do it and that was confusing others...)
Go to your story. (I'd recommend you bookmark your Author page, if you are concerned about too many clicks). It'll have great big bars on top if you have chapters added, but not published. If you have not published a chapter to the story inside of the min time between chapters (currently 24 hours), then you'll be able to publish immediately by pressing publish chapter. (it brings back up the publish dialog box)
This change was made because too many people were screwing up adding chapters, then editing them. It has been the root cause of a bug for the last 10 years at least, where author would post something, set a date a week in advance and then edit 2 or 3 times because they didn't like how the chapter looked. It would randomly break things. This change prevents that because you can now post into the system, make the chapter look the way you want, or do a final proofread before publishing or whatever. Then when it is ready, you press publish. Although you have the option to toggle publish when you add the chapter, that is only for authors not in the Mod Queue. If you are still in moderation, that's not an option since the chapter needs to be approved prior to publishing publicly.