Revert "Bump SDK Extension version to 16" Revert submission 30742572-ext-v16-4 Reason for revert: Need to re-do finalization for Rb changes: https://buganizer.corp.google.com/issues/379269157#comment17 Reverted changes: /q/submissionid:30742572-ext-v16-4 Change-Id: I11eb26917b616ed77d619211e22c6286d3242e71