Delete any old snapshots in path, if not kept.

def deleteUnused(self):
        """ Delete any old snapshots in path, if not kept. """
        (count, size) = (0, 0)

        for (diff, path) in self.extraKeys.items():
            if path.startswith("/"):
                continue

            keyName = self._keyName(diff.toUUID, diff.fromUUID, path)

            count += 1
            size += diff.size

            if self._skipDryRun(logger, 'INFO')("Trash: %s", diff):
                continue

            try:
                self.bucket.copy_key(theTrashPrefix + keyName, self.bucket.name, keyName)
                self.bucket.delete_key(keyName)
            except boto.exception.S3ResponseError as error:
                logger.error("%s: %s", error.code, error.message)

            try:
                keyName = os.path.dirname(keyName) + Store.theInfoExtension
                self.bucket.copy_key(theTrashPrefix + keyName, self.bucket.name, keyName)
                self.bucket.delete_key(keyName)
            except boto.exception.S3ResponseError as error:
                logger.debug("%s: %s", error.code, error.message)

        logger.info("Trashed %d diffs (%s)", count, humanize(size))