oniro-image.bbclass: Avoid empty IMAGE_BOOT_FILES warning

Many targets we support don't use IMAGE_BOOT_FILES which is specific to
the bootfiles wic plugin. Checking for this variable on targets that
don't even use that plugin, makes no sense. Let's drop it for now.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

meta-oniro-core/classes/oniro-image.bbclass

@@ -118,7 +118,6 @@ python deploy_boot_artifacts_to_rootfs() {
     if not boot_files:
         # Nothing to do if IMAGE_BOOT_FILES is not defined. Custom wic plugins
         # are not supported.
-        bb.warn('IMAGE_BOOT_FILES empty, so no boot files will be included in the rootfs')
         return
     deploy_dir = d.getVar('DEPLOY_DIR_IMAGE')
     rootfs_dir = d.getVar('IMAGE_ROOTFS')