Do only single var decl per statement in folly/test/DynamicConverterTest.cpp
Do only single var decl per statement in folly/test/DynamicConverterTest.cpp

Summary: [Folly] Do only single var decl per statement in `folly/test/DynamicConverterTest.cpp`.

Reviewed By: igorsugak

Differential Revision: D9653672

fbshipit-source-id: 08bb529cc90761c69dabd2e00f58f1767f07146a

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly