switch to using android-base/file.h instead of android-base/test_utils.h

Test: compile
Bug: 119313545
Change-Id: I664fb32522d01909c603d7b903475c4e9aea9223
diff --git a/tests/unit/dirutil_test.cpp b/tests/unit/dirutil_test.cpp
index 1ca786c..4dd111a 100644
--- a/tests/unit/dirutil_test.cpp
+++ b/tests/unit/dirutil_test.cpp
@@ -20,7 +20,7 @@
 
 #include <string>
 
-#include <android-base/test_utils.h>
+#include <android-base/file.h>
 #include <gtest/gtest.h>
 
 #include "otautil/dirutil.h"