staging: rtl8192u: Remove commented header.

This patch removes the commented header <linux/config.h>
as it is not used in modern linux systems.

Signed-off-by: Navya Sri Nizamkari <navyasri.tech@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>