greybus: remove unused connection device type

The connection device type is no longer used.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/greybus.h

@@ -164,7 +164,6 @@ extern struct device_type greybus_endo_type;
 extern struct device_type greybus_module_type;
 extern struct device_type greybus_interface_type;
 extern struct device_type greybus_bundle_type;
-extern struct device_type greybus_connection_type;
 
 static inline int is_gb_endo(const struct device *dev)
 {