Remove unused __device__ variable in snn_gpu.cu
Remove unused __device__ variable in snn_gpu.cu

UCI-CARL/CARLsim4,UCI-CARL/CARLsim4,UCI-CARL/CARLsim4,UCI-CARL/CARLsim4,UCI-CARL/CARLsim4,UCI-CARL/CARLsim4