remove ITrainer interface since parameters for train is already getting out of...

remove ITrainer interface since parameters for train is already getting out of sync. Currently there is no benefit of having a interface.

python/paddle/v2/trainer.py

@@ -8,7 +8,7 @@ from . import event as v2_event
 from . import optimizer as v2_optimizer
 from . import parameters as v2_parameters
 
-__all__ = ['ITrainer', 'SGD']
+__all__ = ['SGD']
 
 
 def default_event_handler(event):
@@ -22,26 +22,7 @@ def default_event_handler(event):
     pass
 
 
-class ITrainer(object):
-    """
-    The interface of Trainer. The only exposed method is `train`.
-    """
-
-    def train(self, reader, topology, parameters, event_handler=None):
-        """
-        train method.
-
-        :param reader:
-        :param topology:
-        :param parameters:
-        :param event_handler:
-        :return:
-        """
-
-        raise NotImplementedError()
-
-
-class SGD(ITrainer):
+class SGD():
     def __init__(self, cost, parameters, update_equation):
         """
         Simple SGD Trainer.