Fix unused private field errors

A recent update to libchrome reveals that we were previously suppressing
warnings about unused private fields.

Bug: 28117776
Change-Id: I75f1eabf090744fd883ffd766da4a9c256d7fd6a
Test: This now compiles.
diff --git a/common/libcurl_http_fetcher.h b/common/libcurl_http_fetcher.h
index d126171..7101aaa 100644
--- a/common/libcurl_http_fetcher.h
+++ b/common/libcurl_http_fetcher.h
@@ -259,7 +259,6 @@
   int low_speed_limit_bps_{kDownloadLowSpeedLimitBps};
   int low_speed_time_seconds_{kDownloadLowSpeedTimeSeconds};
   int connect_timeout_seconds_{kDownloadConnectTimeoutSeconds};
-  int num_max_retries_;
 
   DISALLOW_COPY_AND_ASSIGN(LibcurlHttpFetcher);
 };
diff --git a/update_engine_client.cc b/update_engine_client.cc
index 20885ae..6ade12c 100644
--- a/update_engine_client.cc
+++ b/update_engine_client.cc
@@ -104,9 +104,6 @@
   // Pointers to handlers for cleanup
   vector<unique_ptr<update_engine::StatusUpdateHandler>> handlers_;
 
-  // Tell whether the UpdateEngine service is available after startup.
-  bool service_is_available_{false};
-
   DISALLOW_COPY_AND_ASSIGN(UpdateEngineClient);
 };
 
diff --git a/update_manager/real_system_provider.h b/update_manager/real_system_provider.h
index f089a29..d6c2e24 100644
--- a/update_manager/real_system_provider.h
+++ b/update_manager/real_system_provider.h
@@ -74,7 +74,7 @@
 
   chromeos_update_engine::HardwareInterface* const hardware_;
   chromeos_update_engine::BootControlInterface* const boot_control_;
-  chromeos_update_engine::LibCrosProxy* const libcros_proxy_;
+  chromeos_update_engine::LibCrosProxy* const libcros_proxy_ ALLOW_UNUSED_TYPE;
 
   DISALLOW_COPY_AND_ASSIGN(RealSystemProvider);
 };