repository: remove storedeltachains from ifilestorage The ifilestorage interface was bootstrapped from requirements of callers outside the storage implementation (revlogs). I believe we even made some members public so they could be part of the interface! Historically, the changegroup code was a gross offender when it came to accessing low-level storage primitives. There are a handful of members on the ifilestorage interface that are/were used only for changegroup code. With the recent refactor of changegroup code and the establishment of a formal API on the storage interface for producing revision deltas, the changegroup code is no longer accessing these low-level primitives related to delta generation directly. Instead, things are abstracted away in the storage implementation. This means we can remove elements from the storage interface that are no longer needed. We start with "storedeltachains." We remove it from the interface. Then we make it a private attribute and update all references. .. api:: storedeltachains has been dropped from ifilestorage interface .. api:: storedeltachains on revlog classes is now _storedeltachains Differential Revision: https://phab.mercurial-scm.org/D4227