Fix compile error when USE_CHROME_NETWORK_PROXY is not set.

A recent CL introduced a compile error when USE_CHROME_NETWORK_PROXY is
not set. This patch removes the extra ).

Bug: None
Test: `mmma system/update_engine`
Change-Id: I79c2af759e829ce14dd6cb7062d29a8882100280
diff --git a/real_system_state.cc b/real_system_state.cc
index b3ec06d..d99e658 100644
--- a/real_system_state.cc
+++ b/real_system_state.cc
@@ -151,7 +151,7 @@
 #if USE_CHROME_NETWORK_PROXY
                           network_proxy_service_proxy_.get()));
 #else
-                          nullptr)));
+                          nullptr));
 #endif  // USE_CHROME_NETWORK_PROXY
 
   // Initialize the UpdateAttempter before the UpdateManager.