Suppress deprecation warnings in related tests

Suppress deprecation warnings in related tests

Summary:
[Folly] Suppress deprecation warnings in related tests.

When a test specifically exercises a marked-deprecated library or a marked-deprecated part of a library, we do not need to see the deprecation warnings - they are noise.

Specifically, `Singleton` and `Subprocess` have tested but marked-deprecated APIs, so we suppress deprecation warnings in those specific test suites.

Reviewed By: andrewjcg

Differential Revision: D4230826

fbshipit-source-id: 937b078029cde492906088caa3a9e5eee449bc12