usb: renesas_usbhs: remove notify_hotplug callback

The notify_hotplug callback was supported in v3.10, but the last user
(armadillo800eva) was removed by the commit 1fa59bda ("ARM: shmobile:
Remove legacy board code for Armadillo-800 EVA"). So, this patch
removes it.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>