sync_backend_host_impl_unittest.cc: Remove dead code.

components/sync/driver/glue/sync_backend_host_impl_unittest.cc

Index: components/sync/driver/glue/sync_backend_host_impl_unittest.cc
diff --git a/components/sync/driver/glue/sync_backend_host_impl_unittest.cc b/components/sync/driver/glue/sync_backend_host_impl_unittest.cc
index dc376d9f2c9fb7a361d983e48d83757cfdf5ea48..2ef2da85192cc29fb1e559f29c3f50856c091732 100644
--- a/components/sync/driver/glue/sync_backend_host_impl_unittest.cc
+++ b/components/sync/driver/glue/sync_backend_host_impl_unittest.cc
@@ -59,10 +59,6 @@ namespace {
 static const base::FilePath::CharType kTestSyncDir[] =
     FILE_PATH_LITERAL("sync-test");
 
-ACTION_P(Signal, event) {
-  event->Signal();
-}
-
 void EmptyNetworkTimeUpdate(const base::Time&,
                             const base::TimeDelta&,
                             const base::TimeDelta&) {}