docs/system/s390x/bootdevices: Update the documentation about network booting

Remove the information about the separate s390-netboot.img from
the documentation.

Co-authored by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Message-ID: <20241020012953.1380075-7-jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed