Remove unused classes MaxPoolForwardBackward and AveragePoolForwardBackward
Remove unused classes MaxPoolForwardBackward and AveragePoolForwardBackward

hvy/chainer,chainer/chainer,hvy/chainer,hvy/chainer,chainer/chainer,niboshi/chainer,niboshi/chainer,chainer/chainer,pfnet/chainer,niboshi/chainer,niboshi/chainer,chainer/chainer,hvy/chainer