arm64: dts: remove s2 regulator from smd regulators.

s2 is spmi controller regulator on msm8916 according to downstream 3.10
kernel, so remove it from the dt to avoid confusion an use of it.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>