Removed assertion that required maxSpikesD1!=0 in snn_gpu.cu.
Removed assertion that required maxSpikesD1!=0 in snn_gpu.cu.

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