Merge "Remove unused use_protobuf3 flag" into main am: d842f5d0

Original change: https://android-review.googlesource.com/c/platform/build/+/2879286



Change-Id: I9c58fb10d9c8345487520ed5f6b19fafa2227e3c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>