remove unnecessary class variable
remove unnecessary class variable

hvy/chainer,chainer/chainer,ronekko/chainer,ktnyt/chainer,rezoo/chainer,chainer/chainer,pfnet/chainer,keisuke-umezawa/chainer,ktnyt/chainer,okuta/chainer,okuta/chainer,wkentaro/chainer,anaruse/chainer,wkentaro/chainer,chainer/chainer,niboshi/chainer,hvy/chainer,chainer/chainer,okuta/chainer,hvy/chainer,okuta/chainer,tkerola/chainer,jnishi/chainer,wkentaro/chainer,niboshi/chainer,wkentaro/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,ktnyt/chainer,niboshi/chainer,niboshi/chainer,hvy/chainer,ktnyt/chainer,jnishi/chainer,jnishi/chainer,keisuke-umezawa/chainer,jnishi/chainer