Fix missing symbol issue

The unit tests exposed a symbol linking issue.

Change-Id: If59707345fda33a6c31b7ed02020c474f6fd30aa
diff --git a/src/core/plugin_registry/grpc_plugin_registry.cc b/src/core/plugin_registry/grpc_plugin_registry.cc
index eb8f14c..3cce1f0 100644
--- a/src/core/plugin_registry/grpc_plugin_registry.cc
+++ b/src/core/plugin_registry/grpc_plugin_registry.cc
@@ -56,7 +56,7 @@
 extern void RegisterResourceQuota(CoreConfiguration::Builder* builder);
 extern void FaultInjectionFilterRegister(CoreConfiguration::Builder* builder);
 extern void RegisterDnsResolver(CoreConfiguration::Builder* builder);
-extern void RegisterBackendMetricFilter(CoreConfiguration::Builder* builder);
+// extern void RegisterBackendMetricFilter(CoreConfiguration::Builder* builder);
 extern void RegisterSockaddrResolver(CoreConfiguration::Builder* builder);
 extern void RegisterFakeResolver(CoreConfiguration::Builder* builder);
 extern void RegisterPriorityLbPolicy(CoreConfiguration::Builder* builder);
@@ -129,7 +129,7 @@
 #endif  // !GRPC_NO_RLS
   // Run last so it gets a consistent location.
   // TODO(ctiller): Is this actually necessary?
-  RegisterBackendMetricFilter(builder);
+  //  RegisterBackendMetricFilter(builder); // DISABLED, Not available in emu-dev
   RegisterSecurityFilters(builder);
   RegisterExtraFilters(builder);
   RegisterBuiltins(builder);