test_efi_plugin_plain_systemd-boot: don't set console

This effectively disables the boot time serial console
so that kernel and initrd logs are not visible which
makes debugging boot failures hard. The logs are
not too verbose, around 270 lines, and can be reduced
with kernel side settings if needed. For example
"loglevel=4" on kernel command line reduces the
output to only warning messages.

(From OE-Core rev: 0469af3bd8e3c721ba9c6f96d786c95a1726368b)

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-selftest/wic/test_efi_plugin_plain_systemd-boot.wks

@@ -2,4 +2,4 @@
 part /boot --source bootimg-efi --sourceparams="loader=systemd-boot,initrd=${INITRAMFS_IMAGE}-${MACHINE}.${INITRAMFS_FSTYPES}" --active --align 1024 --use-uuid
 part / --source rootfs --fstype=ext4 --align 1024 --use-uuid
 
-bootloader  --timeout=0 --append="console=ttyS0,115200n8"
+bootloader  --timeout=0