USB: phy: drop unused legacy controller-phy bind helper

Drop the unused legacy usb_bind_phy() helper whose last user was removed
in 2016 when OMAP moved to device-tree boot (9080b8dc ("ARM: OMAP2+:
Remove legacy usb-host.c platform init code")).

Note that this means that for the last couple of years the phy_bind_list
has been empty (when using mainline kernels) and that consequently all
phy lookups using the usb_get_phy_dev() interface have failed with
-ENODEV. This helper along with its current users will be removed by
follow-on patches.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>