ARM: EXYNOS4: Remove meaningless REGULATOR config option

The regulator API ifdefs itself out when not enabled
so there is no need for users to do this.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
[kgene.kim@samsung.com: edited description]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>