Remove use_gpu and trainer_count in train.py

Author: wanghaoshuang

demo/recognize_digits/train.py

@@ -100,7 +100,7 @@ def convolutional_neural_network(img):
 
 
 def main():
- paddle.init(use_gpu=False, trainer_count=1)
+ paddle.init()
 
  # define network topology
  images = paddle.layer.data(