ARM: dts: Remove unused bootargs from exynos3250-rinato

This patch removes unused dt node of command line from Exynos3250-based
Rinato board because kernel use the command line from bootloader.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>