hw/intc/armv7m_nvic.c: Remove out of date comment

hw/intc/armv7m_nvic.c: Remove out of date comment

Remove an out of date comment which says there's only one
item in the NVIC container region -- we put systick into its
own device object a while back and so now there are two
things in the container.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1501692241-23310-6-git-send-email-peter.maydell@linaro.org