remove duplicated macro (#29563)

paddle/fluid/operators/math/prelu.cu

@@ -20,11 +20,6 @@ namespace math {
 
 #define CUDA_NUM_THREADS 1024
 
-// CUDA: grid stride looping
-#define CUDA_KERNEL_LOOP(i, n)                                    \
-  for (size_t i = blockIdx.x * blockDim.x + threadIdx.x; i < (n); \
-       i += blockDim.x * gridDim.x)
-
 inline static int PADDLE_GET_BLOCKS(const int N) {
   return (N + CUDA_NUM_THREADS - 1) / CUDA_NUM_THREADS;
 }