Fix bad merge.

Summary:
FBStringTest.cpp was refactored, but the TestUtil and
TemporaryFile was not properly removed.

Reviewed By: yfeldblum

Differential Revision: D2913045

fb-gh-sync-id: 710c3f5b808acb634dfcd65219484ddc257ed52c

folly/test/FBStringTest.cpp

@@ -33,7 +33,6 @@
 #include <folly/Portability.h>
 #include <folly/Random.h>
 #include <folly/Conv.h>
-#include <folly/experimental/TestUtil.h>
 
 using namespace std;
 using namespace folly;