recipes-kernel: Remove all Xavier AGX and NX devkits related code

These devices are in progress of being released on JP5,
from a different repository: https://github.com/balena-os/balena-jetson-jp5

Signed-off-by: Alexandru Costache <alexandru@balena.io>

layers/meta-balena-jetson/recipes-kernel/linux/kernel-image-initramfs.bbappend

@@ -1,20 +1,3 @@
-# For Xavier devices, which don't use
-# u-boot and load the kernel from a raw
-# partition, we can free up some rootfs
-# space that would otherwise be taken up by
-# the kernel image.
-do_install:append:jetson-xavier() {
-    echo "" > ${D}/boot/${type}
-}
-
-do_install:append:jetson-xavier-nx-devkit-emmc() {
-    echo "" > ${D}/boot/${type}
-}
-
-do_install:append:jetson-xavier-nx-devkit() {
-    echo "" > ${D}/boot/${type}
-}
-
 # Fixes error: packages already installed
 # by kernel-image-initramfs
 do_install:append() {