Remove _CRT_SECURE_NO_WARNINGS from testArchUtil

 `_CRT_SECURE_NO_WARNINGS` is defined in two places on Windows.
This yields the following warning when building `testArchUtil`.

```
testArchUtil.cpp(7): warning C4005: '_CRT_SECURE_NO_WARNINGS': macro redefinition
testArchUtil.cpp: note: see previous definition of '_CRT_SECURE_NO_WARNINGS'
```

This PR removes the unneeded `_CRT_SECURE_NO_WARNINGS`.  It's not clear what warning `_CRT_SECURE_NO_WARNINGS` was being introduced to suppress in `testArchUtil` as disabling both the `#define` and `msvcdefaults.cmake` doesn't yield any additional warnings in `testArchUtil`.

Closes #3885

(Internal change: 2387624)

Author: nvmkuruc

pxr/base/arch/testenv/testArchUtil.cpp

@@ -4,8 +4,6 @@
 // Licensed under the terms set forth in the LICENSE.txt file available at
 // https://openusd.org/license.
 //
-#define _CRT_SECURE_NO_WARNINGS
-
 #include "pxr/pxr.h"
 #include "pxr/base/arch/testArchUtil.h"
 #include "pxr/base/arch/attributes.h"