SubprocessTest does not use dirent.h

Summary: Remove it as we do not need it here.

Reviewed By: yfeldblum

Differential Revision: D3365991

fbshipit-source-id: bb36caca0319df4c8d6e3d978045b7c28369f043

folly/test/SubprocessTest.cpp

@@ -31,7 +31,6 @@
 #include <folly/gen/String.h>
 #include <folly/experimental/TestUtil.h>
 #include <folly/experimental/io/FsUtil.h>
-#include <folly/portability/Dirent.h>
 #include <folly/portability/Unistd.h>
 
 using namespace folly;