linux-yocto: remove signing

Remove secure boot signature from kernel image.
It's signed as part of uki image now which signs
kernel, initramfs etc.

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm/recipes-kernel/linux/linux-yocto-uefi-secureboot.inc

@@ -1,14 +1,4 @@
 KERNEL_FEATURES += "cfg/efi-ext.scc"
 
-inherit sbsign
-
-# shell variable set inside do_compile task
-SBSIGN_TARGET_BINARY = "$KERNEL_IMAGE"
-
-do_compile:append() {
-    KERNEL_IMAGE=$(find ${B} -name ${KERNEL_IMAGETYPE} -print -quit)
-    do_sbsign
-}
-
 RRECOMMENDS:${PN} += "kernel-module-efivarfs"
 RRECOMMENDS:${PN} += "kernel-module-efivars"