Drop an unused function in iso9600.py

from diffoscope.difference import Difference

from .utils.file import File

from .utils.command import Command, our_check_output

from .utils.command import Command

from .utils.libarchive import LibarchiveContainerWithFilelist

@tool_required("isoinfo")

def get_iso9660_names(path):

    return (

        our_check_output(

            (

                "isoinfo",

                "-R",  # Always use RockRidge for names

                "-f",

                "-i",

                path,

            ),

        )

        .strip()

        .split("\n")

    )

class ISO9660PVD(Command):

    @tool_required("isoinfo")

    def cmdline(self):