mfd: arizona: Drop arizona-extcon cells

The arizona jack-dection handling is being reworked so that the
codec-child-device drivers directly handle jack-detect themselves,
so it is no longer necessary to instantiate "arizona-extcon"
child-devices.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Tested-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>