Fix //third_party/cec to not disable -Wunused-function.

ui/aura/mus/window_tree_client.cc

Index: ui/aura/mus/window_tree_client.cc
diff --git a/ui/aura/mus/window_tree_client.cc b/ui/aura/mus/window_tree_client.cc
index 5b2cd4c304b8a336c95413b38e2ea031c8a4875b..793a10fbfd6d709521016a96a07bc34fd5e14ab7 100644
--- a/ui/aura/mus/window_tree_client.cc
+++ b/ui/aura/mus/window_tree_client.cc
@@ -64,10 +64,6 @@ inline uint16_t HiWord(uint32_t id) {
   return static_cast<uint16_t>((id >> 16) & 0xFFFF);
 }
 
-inline uint16_t LoWord(uint32_t id) {
-  return static_cast<uint16_t>(id & 0xFFFF);
-}
-
 struct WindowPortPropertyDataMus : public WindowPortPropertyData {
   std::string transport_name;
   std::unique_ptr<std::vector<uint8_t>> transport_value;