usb: gadget: android: Honor CONFIG_USB_GADGET_VBUS_DRAW

The maximum current draw was hard coded to 500 mA.  composite.c
has code that uses CONFIG_USB_GADGET_VBUS_DRAW to set the
bMaxPower and to set whether or not the device is self-powered if
they haven't been set.  This change removes the code in android.c
to allow composite.c to set them.

Change-Id: I9db37922e91ee86e9e5c0e14519e119e5c41ca48
Signed-off-by: Scott Anderson <saa@google.com>