Revert "unpack_bootimg: Export 'vendor_ramdisk' for vendor_boot v4" am: f85a2fd564 am: ccf44dde20 am: fa9f1fa517

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

Change-Id: I65be08af83769ba03301cb4b30b4f141b3974e38
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>