avutil/utf8: put under #ifdef TEST

All other test programs are under #ifdef TEST too
with the implementation and test code being generally in the same file
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/utf8.c

@@ -18,6 +18,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#ifdef TEST
 #include <stdio.h>
 
 #include "libavutil/avstring.h"
@@ -69,3 +70,4 @@ int main(int argc, char **argv)
     av_file_unmap(file_buf, file_buf_size);
     return 0;
 }
+#endif