test: remove unecessary using namespace
test: remove unecessary using namespace

Summary: This breaks the build, remove it.

Reviewed By: fanzeyi

Differential Revision: D36494327

fbshipit-source-id: 9078fef5ab0a5c6d009906fa65d6f71f2c7227ee

facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman