Delete any old partial uploads/downloads in path.

def deletePartials(self, dryrun=False):
        """ Delete any old partial uploads/downloads in path. """
        for (vol, path) in self.extraVolumes.items():
            if not path.endswith(".part"):
                continue
            if self._skipDryRun(logger, 'INFO', dryrun=dryrun)("Delete subvolume %s", path):
                continue
            self.butterVolumes[vol.uuid].destroy()