arm64: dts: allwinner: pinephone: Remove AC power supply

The AXP803 in the Pinephone has its ACIN and VBUS pins shorted together.
In this configuration, the VBUS control registers take priority over the
ACIN control registers, which means the ACIN sysfs knobs have no effect.
Remove the AC power supply from the DTS, since VBUS is really the only
power supply.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201105054135.24860-2-samuel@sholland.org