Remove usage of commonId of discussion messages at the FE

[elatif2020]

We realized that it doesn't make sense to store the commonId for each discussion message.
We should remove it. Here is the corresponding BE ticket https://github.com/daostack/common-backend/issues/2272
Need to figure out where is it being used in the FE, and whether we have a good alternative implementation everywhere (or some BE changes are needed)