jffs2: Remove C++ style comments from uapi header

Linux kernel tolerates C++ style comments these days. Actually, the
SPDX License tags for .c files start with //.

On the other hand, uapi headers are written in more strict C, where
the C++ comment style is forbidden.

I simply dropped these lines instead of fixing the comment style.

This code has been always commented out since it was added around
Linux 2.4.9 (i.e. commented out for more than 17 years).

'Maybe later...' will never happen.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Richard Weinberger <richard@nod.at>