sh: delete redundant CONFIG_SH definition

CONFIG_SH is defined in arch/sh/config.mk.
It is not necessary to define it in each board
header config header file.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>