sysmocom-bsc-directimage: revert syslinux changes

* setting APPEND in the image file overwrites
  the APPEND from boot-directdisk.bbclass in edison, which
  creates the syslinux.cfg without "root=" stanza

* for dora we do not use syslinux or the image-directdisk
  so revert this paticular changes

Fixes: SYS#373

recipes-apps/images/sysmocom-bsc-ip-image-directdisk.bb

@@ -6,15 +6,5 @@ LICENSE = "MIT"
 
 inherit boot-directdisk
 
-SYSLINUX_ROOT = "root=/dev/sda2"
-SYSLINUX_PROMPT = "0"
-SYSLINUX_TIMEOUT = "2"
-SYSLINUX_SERIAL = "0 38400"
-SYSLINUX_SERIAL_TTY = "console=ttyS0,38400"
-SYSLINUX_LABELS = "boot"
-APPEND = "${SYSLINUX_SERIAL_TTY} net.ifnames=0"
-LABELS_append = " ${SYSLINUX_LABELS} "
-
-
 ROOTFS = "${DEPLOY_DIR_IMAGE}/sysmocom-bsc-ip-image-${MACHINE}.ext4"
 do_bootdirectdisk[depends] += "sysmocom-bsc-ip-image:do_rootfs"