Remove stray FXL dependency

Change-Id: I347a539462cfbfd511e787baedfbfb6e122d9af4
diff --git a/filesystem/tests/file_descriptor_unittest.cc b/filesystem/tests/file_descriptor_unittest.cc
index efb844f..be26df3 100644
--- a/filesystem/tests/file_descriptor_unittest.cc
+++ b/filesystem/tests/file_descriptor_unittest.cc
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "lib/fxl/portable_unistd.h"
-
 #include <fcntl.h>
 #include <sys/types.h>