Refine ExpandConvLayer.cpp

[hedaoyuan]

Based on previous code refactoring #2282, the file ExpandConvTransLayer has been removed. By further refactoring the convolution layer of im2col + gemm, we can remove the ExpandConvBaseLayer file.

• The addSharedBias and bpropSharedBias implementation in the ExpandConvBaseLayer is less performance, we can use Matrix::addSharedBias and Matrix::collectSharedBias to replace.
• After removing the four functions related to the bias operation, ExpandConvBaseLayer has only one init function, so we can further refactor to remove this class.