Supress proguard warnings for GooglePlayServicesUtil.
Supress proguard warnings for GooglePlayServicesUtil.

This fixes release builds that run proguard twice, once on the
library and once on the APK.

BUG=504009
TBR=tedchoc@chromium.org

Review URL: https://codereview.chromium.org/1210173007.

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#336927}

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