Remove DocState::LocallyCreatedButNotEdited

[alexjg]

The main reason to remove this is that it's a bit of a footgun. If you don't save or announce documents until some changes have been made then the user has to keep track of whether they have made changes before they know if it's safe to share the document ID with other peers. A concrete example of this which we encountered in the JS implementation was a tab creating a document on startup and putting the ID of the document in the URL. This meant that if you copied the URL to another tab but the first tab hadn't made any changes then the second tab just hung forever.

Empty documents take up a tiny amount of space, it seems worth trading that very small amount of extra space to avoid the user having to keep track of whether they have made changes to a document before they can advertise it's ID.