USB: OTG: remove pm8921_set_usb_power_supply_type

This custom notifier is no longer required to determine
wether a wall charger is connected to the PM8921 charger
or not.

The pm8921-charger driver determines AC charging solely
dependent upon maximum input current from the charging
device.

CRs-Fixed: 339841
Change-Id: I564fa01c61286d013be6b263d038e87568a297f2
Signed-off-by: David Keitel <dkeitel@codeaurora.org>