Remove output error parameter from BuildDeviceResource

This method never fails.

Change-Id: If7c385f967e943172fa97e98c2c1c4e18a5cdc8f
Reviewed-on: https://weave-review.googlesource.com/1798
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
diff --git a/src/device_registration_info.h b/src/device_registration_info.h
index f3b5302..ff9c29b 100644
--- a/src/device_registration_info.h
+++ b/src/device_registration_info.h
@@ -247,7 +247,7 @@
   // Builds Cloud API devices collection REST resource which matches
   // current state of the device including command definitions
   // for all supported commands and current device state.
-  std::unique_ptr<base::DictionaryValue> BuildDeviceResource(ErrorPtr* error);
+  std::unique_ptr<base::DictionaryValue> BuildDeviceResource() const;
 
   void SetGcdState(GcdState new_state);
   void SetDeviceId(const std::string& cloud_id);