Removes all saved links except the ones that are used.

        Args:
            used (list): list of used links that should not be removed.

def remove_unused_links(self, used):
        """Removes all saved links except the ones that are used.

        Args:
            used (list): list of used links that should not be removed.
        """
        unused = []

        self._execute("SELECT * FROM {}".format(self.LINK_STATE_TABLE))
        for row in self.cursor:
            relpath, inode, mtime = row
            inode = self._from_sqlite(inode)
            path = os.path.join(self.root_dir, relpath)

            if path in used:
                continue

            if not os.path.exists(path):
                continue

            actual_inode = get_inode(path)
            actual_mtime, _ = get_mtime_and_size(path)

            if inode == actual_inode and mtime == actual_mtime:
                logger.debug("Removing '{}' as unused link.".format(path))
                remove(path)
                unused.append(relpath)

        for relpath in unused:
            cmd = 'DELETE FROM {} WHERE path = "{}"'
            self._execute(cmd.format(self.LINK_STATE_TABLE, relpath))