Drop support for Renesas H8/300 (h8300) architecture

H8/300 has been dead for several years, and the kernel for it
has not compiled for ages. Drop support for it.

Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>