Deshim TestUtil in openr

Summary:
The following rules were deshimmed:
```
//folly/experimental:test_util -> //folly/testing:test_util
```

The following headers were deshimmed:
```
folly/experimental/TestUtil.h -> folly/testing/TestUtil.h
```

This is a codemod. It was automatically generated and will be landed once it is approved and tests are passing in sandcastle.
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p:detuv.openr

Reviewed By: praihan

Differential Revision: D58833743

fbshipit-source-id: f5aaee1d3dfb13e7551c355becf8a78a2884132b

openr/config/tests/ConfigTest.cpp

@@ -6,7 +6,7 @@
  */
 
 #include <folly/FileUtil.h>
-#include <folly/experimental/TestUtil.h>
+#include <folly/testing/TestUtil.h>
 #include <glog/logging.h>
 #include <gtest/gtest.h>