docs: Can leave StrictMode enabled in prod

Google Play now checks StrictMode elements based on target SDK
version, so it's safe for apps to leave StrictMode checks enabled in
their production code.

Bug: 179525953
Change-Id: I5a68d4892d521f5e62c25f57621f934c39436008
Test: m ds-docs-java
Exempt-From-Owner-Approval: Docs-only change