art: use proper nativehelper headers

libnativeheader exports headers under nativeheader. These were
available before incorrectly as global headers in order to give
access to jni.h.

Test: modules using art find headers
Bug: 63762847
Change-Id: I5c820d677e94e07b2859e78610bc997fe51b41dc
diff --git a/runtime/native/libcore_util_CharsetUtils.cc b/runtime/native/libcore_util_CharsetUtils.cc
index 38634e6..c698548 100644
--- a/runtime/native/libcore_util_CharsetUtils.cc
+++ b/runtime/native/libcore_util_CharsetUtils.cc
@@ -18,14 +18,13 @@
 
 #include <string.h>
 
-#include "nativehelper/jni_macros.h"
-
 #include "jni_internal.h"
-#include "mirror/string.h"
 #include "mirror/string-inl.h"
+#include "mirror/string.h"
 #include "native_util.h"
+#include "nativehelper/ScopedPrimitiveArray.h"
+#include "nativehelper/jni_macros.h"
 #include "scoped_fast_native_object_access-inl.h"
-#include "ScopedPrimitiveArray.h"
 #include "unicode/utf16.h"