power: smb1351: Remove otg_vreg support for charger

In the current deign, it is expected for the charger driver
to detect OTG and enable it without the USB driver to
explicitly enable it. As this support exists in the driver,
remove the OTG regulator configuration.

Change-Id: I165b144a2a8be88b493142de3a4a645e07f06253
Signed-off-by: Kavya Nunna <knunna@codeaurora.org>