usb: Kconfig: remove unneeded default value

If no default value is specified, then 'n' is used so the default value
used here is not needed. Furthermore, we should never change default
values depending on EXPERT mode. EXPERT mode should only make options
visible, not change them.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>