json-c: Remove icecc specific comment

json-c: Remove icecc specific comment

6481e8b209b ("json-c: fix icecc compilation") disabled '-Werror' unconditionally
for all compilers. We want to keep it disabled to reduce efforts when updating
or adding support for new toolchains (see [0]), but since support for icecc has
been removed via ba4fd5229893 ("classes/recipes-devtools: Drop icecc from
OE-Core") recently, we can drop the comment referencing it.

[0]: https://lists.openembedded.org/g/openembedded-core/message/219364

Signed-off-by: Moritz Haase <Moritz.Haase@bmw.de>
CC: quentin.schulz@cherry.de
CC: m.felsch@pengutronix.de
CC: ross.burton@arm.com
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>