Use protobuf 2.x instead of 3.x

Ignore-AOSP-First: Will be merged into AOSP shortly after merging here.
    Merging here first as the topic includes fixes to internal-only
    projects.
Bug: 270895633
Test: build
Change-Id: I05c3b687e1db1a240d2a96b5f0005ba5d0934ce8