[MERGE] nuke ``VersionedFile.create_empty``

[Ian Clatworthy]

Robert Collins wrote:
> This is a real problem for being able to stack things, so I'm not
> deprecating, I'm removing.

bb:approve

My only concern here is the potential performance impact of

             for index, version in enumerate(order):
                 pb.update('Converting versioned data', index, total)
+                if version in target:
+                    continue

For VersionFiles with many revisions (e.g. inventories on projects with
deep history), this could suck. I'm not sure how often this default join
logic gets triggered.

Is it worth pre-filtering the order list so the need for this test goes
away? If so, that can come in another patch IMO.

Ian C.