MAINTAINERS: drop Vincent Sanders from Simtec S3C boards

Vincent Sanders' email bounces with code 550 (user does not exist) so
remove the entry from Simtec S3C24xx boards.

Cc: Simtec Linux Team <linux@simtec.co.uk>
Cc: linux-samsung-soc@vger.kernel.org
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>