ARM: dts: sun9i: cubieboard4: Drop sunxi-common-regulators.dtsi

sunxi-common-regulators.dtsi provided dummy regulators vcc3v0, vcc3v3,
vcc5v0. 3.0V/3.3V and 5.0V are commonly used voltages in Allwinner
devices. These dummy regulators provide a stand-in when bindings that
require one, but the real regulator is not supported yet.

Since these are no longer needed, we can drop the include file.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>