vfs: drop the 'mustaudit' API There are no remaining users of 'mustaudit' so we can safely drop the API. External user are unlikely from a quick research so no deprecation is added.

streamclone: stop using 'vfs.mustaudit = False' Now that each call disable the auditing on its own, we can safely drop this the mustaudit usage. No other code is modified.

vfs: simplify path audit disabling in stream clone The whole 'mustaudit' API is quite complex compared to its actual usage by its unique user in stream clone. Instead we add a "auditpath" parameter to 'vfs.__call_'. The stream clone code then explicitly open files with path auditing disabled. The 'mustaudit' API will be cleaned up in the next changeset.