Remove unused destructor

mlx/backend/cuda/device.cpp

@@ -189,8 +189,6 @@ CommandEncoder::CommandEncoder(Device& d)
   CHECK_CUDA_ERROR(cudaGraphCreate(&graph_, 0));
 }
 
-CommandEncoder::~CommandEncoder() = default;
-
 void CommandEncoder::add_completed_handler(std::function<void()> task) {
   worker_.add_task(std::move(task));
 }

mlx/backend/cuda/device.h

@@ -32,7 +32,6 @@ class CommandEncoder {
   };
 
   explicit CommandEncoder(Device& d);
-  ~CommandEncoder();
 
   CommandEncoder(const CommandEncoder&) = delete;
   CommandEncoder& operator=(const CommandEncoder&) = delete;