remove vector::erase

[chengduoZH]

fix #5792

[typhoonzero]

col_shape_vec[0] = input->dims()[1] / groups should be fine.

[chengduoZH]

It doesn't get what we want.

  std::vector<int> vec_i({ 501, 502, 503 });

  std::vector<int> vec (8);
  vec[0]  = 12;
  vec.insert(vec.begin()+1, vec_i.begin(), vec_i.end());

If we write it in this way, vec is {12 501 502 503 0 0 0 0 0 0 0}.
But if we write it in the other way, vec is {12 501 502 503}.

  std::vector<int> vec (8);
  vec.assign(1, 12);
  vec.insert(vec.begin()+1, vec_i.begin(), vec_i.end());

[typhoonzero]

LGTM++