repack_bootimg: replaces the ramdisk file directly am: d0d261f3b0 am: 0639d39c12 am: d6c8be1c86 am: 21e91e2a7a am: 43552e584a

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/1696925

Change-Id: I725d915aef74330b46efc660b929d6a7f8488f08