extcon: palmas: remove unused member from palams_usb structure

Remove unused member vbus_enable and set_vbus_work from palmas_usb
as these members are not used in drivers.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Acked-by: Graeme Gregory <gg@slimlogic.co.uk>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>