Fix unittest

Author: reyoung

paddle/gserver/tests/sequence_nest_layer_group.conf

@@ -51,8 +51,7 @@ def lstm_group(lstm_group_input):
         size=hidden_dim,
         act=TanhActivation(),
         gate_act=SigmoidActivation(),
-        state_act=TanhActivation(),
-        lstm_layer_attr=ExtraLayerAttribute(error_clipping_threshold=50))
+        state_act=TanhActivation())
     return lstm_output