select_tut.2: Adjust header file includes in example

Employ <sys/select.h>, rather than the historical header files.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/select_tut.2

@@ -354,8 +354,7 @@ from one TCP port to another.
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
-#include <sys/time.h>
-#include <sys/types.h>
+#include <sys/select.h>
 #include <string.h>
 #include <signal.h>
 #include <sys/socket.h>