power: pm8921-charger: remove set_usb_power_supply_type

This custom API is no longer required since AC charging
reporting to userspace is solely dependent on the maximum
current supplied by the USB rather than the connector
type.

CRs-Fixed: 339841
Change-Id: Id542b083dd4f0ba5679d64f9e20d3b04cf14d972
Signed-off-by: David Keitel <dkeitel@codeaurora.org>