Revert "unpack_bootimg: Export 'vendor_ramdisk' for vendor_boot v4" am: f85a2fd564 am: ccf44dde20 am: fa9f1fa517 am: a6cff18639 am: 37c940dc01

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

Change-Id: I21b13ff2314010a2ebbc219c8e70f324a39f9803
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>