Fix memory leak in wangle/channel/test:FileRegionTest.
Fix memory leak in wangle/channel/test:FileRegionTest.

Summary: ... as titled.

Reviewed By: anirudhvr

Differential Revision: D6596347

fbshipit-source-id: 8e01144f853cb49ea825a84e648b2d909a1d75d4

facebook/wangle,facebook/wangle,facebook/wangle