sysutils/usbtop: unbreak with boost 1.69

In file included from src/console_output.cpp:31:
In file included from include/usbtop/buses.h:34:
In file included from include/usbtop/usb_bus.h:34:
In file included from include/usbtop/usb_device.h:35:
include/usbtop/usb_stats.h:44:21: error: expected class name
class Stats: boost::noncopyable

^

include/usbtop/usb_stats.h:84:24: error: expected class name
class UsbStats: boost::noncopyable

^

In file included from src/console_output.cpp:31:
In file included from include/usbtop/buses.h:34:
In file included from include/usbtop/usb_bus.h:34:
include/usbtop/usb_device.h:41:25: error: expected class name
class UsbDevice: boost::noncopyable

^

In file included from src/console_output.cpp:31:
In file included from include/usbtop/buses.h:34:
include/usbtop/usb_bus.h:45:22: error: expected class name
class UsbBus: boost::noncopyable

^

PR: 232525