USB: fix char-device disconnect handling

This patch (as1198) fixes a conceptual bug: Somewhere along the line
we managed to confuse USB class devices with USB char devices.  As a
result, the code to send a disconnect signal to userspace would not be
built if both CONFIG_USB_DEVICE_CLASS and CONFIG_USB_DEVICEFS were
disabled.

The usb_fs_classdev_common_remove() routine has been renamed to
usbdev_remove() and it is now called whenever any USB device is
removed, not just when a class device is unregistered.  The notifier
registration and unregistration calls are no longer conditionally
compiled.  And since the common removal code will always be called as
part of the char device interface, there's no need to call it again as
part of the usbfs interface; thus the invocation of
usb_fs_classdev_common_remove() has been taken out of
usbfs_remove_device().

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Alon Bar-Lev <alon.barlev@gmail.com>
Tested-by: Alon Bar-Lev <alon.barlev@gmail.com>
Cc: stable <stable@kernel.org>