Revert "unpack_bootimg: Export 'vendor_ramdisk' for vendor_boot v4" am: f85a2fd564

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/2181573

Change-Id: Ie709e621aae571ca223695cf1c7300660190be68
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>