Delete unused mutex in HWC2to1Adapter

    class DeferredFence {

        public:

            DeferredFence()

              : mMutex(),

                mFences({Fence::NO_FENCE, Fence::NO_FENCE}) {}

              : mFences({Fence::NO_FENCE, Fence::NO_FENCE}) {}

            void add(int32_t fenceFd) {

                mFences.emplace(new Fence(fenceFd));

            }

        private:

            mutable std::mutex mMutex;

            std::queue<sp<Fence>> mFences;

    };