machine-xilinx-default.inc: Remove image_types_uboot
This has changed in the meta layer and breaks the build, as it appears
it is no longer required just remove it.
@@ -7,7 +7,6 @@ MACHINE_FEATURES_BACKFILL_CONSIDERED_append_microblaze = " qemu-usermode"
# File System Configuration
IMAGE_FSTYPES ?= "tar.gz cpio cpio.gz.u-boot"
-IMAGE_CLASSES += "image_types_uboot"
# Kernel Configuration
XILINX_DEFAULT_KERNEL := "linux-xlnx"
