extcon: axp288: Remove usb_phy notification code

The usb_phy based intel-usb-phy code never got merged into the
mainline kernel, so the devm_usb_get_phy() call will always fail,
blocking the driver from loading.

Since new drivers should use the generic-phy framework, not the
old-style usb_phy stuff, keeping this around is not useful.

Therefor this patch removes the usb_phy notification bits, which together
with the patch to remove the platform_data dependency, makes this driver
actually successfully probe on systems with an axp288 pmic.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>