Save build.prop files when trimming OTA/target_files am: f3f85a1c1a am: 3a3c797f61

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2123560

Change-Id: I96bbc07d0add19ff1d398660b228df51fb3c14bc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>