Remove redundancy codes

Author: gaoyuan

doc/api/v2/config/layer.rst

@@ -110,7 +110,7 @@ sum_to_one_norm
     :noindex:
 
 cross_channel_norm
----------------
+------------------
 ..  automodule:: paddle.v2.layer
     :members: cross_channel_norm
     :noindex:

paddle/gserver/layers/CrossChannelNormLayer.cpp

@@ -78,7 +78,6 @@ void CrossChannelNormLayer::backward(const UpdateCallback& callback) {
   Matrix::resizeOrCreate(sampleBuffer_, channels_, spatialDim, false, useGpu_);
   scaleDiff_->zeroMem();
   for (size_t i = 0; i < batchSize; i++) {
-    spatialBuffer_->zeroMem();
     // propagate to param.
     MatrixPtr dataBufferTmp =
         Matrix::create(dataBuffer_->getData() + i * dataDim,

paddle/gserver/layers/NormLayer.h

@@ -68,7 +68,7 @@ class ResponseNormLayer : public NormLayer {
 /**
  * This layer applys normalization across the channels of each sample to a
  * conv layer's output, and scales the output by a group of trainable factors
- * whose equal to the number of channels.
+ * whose dimensions equal to the number of channels.
  * - Input: One and only one input layer are accepted.
  * - Output: The normalized data of the input data.
  * Reference: