scripts: remove bin2c

Commit 80f8be7a ("tomoyo: Omit use of bin2c") removed the last
use of bin2c.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>