remove plot_curve in v2.__init__ to avoid importing matplotlib when test

python/paddle/v2/__init__.py

@@ -29,12 +29,11 @@ import inference
 import networks
 import py_paddle.swig_paddle as api
 import minibatch
-import plot_curve
 
 __all__ = [
     'optimizer', 'layer', 'activation', 'parameters', 'init', 'trainer',
     'event', 'data_type', 'attr', 'pooling', 'data_feeder', 'dataset', 'reader',
-    'topology', 'networks', 'infer', 'plot_curve'
+    'topology', 'networks', 'infer'
 ]