Remove entries in multichain_addresses.csv of univ2 forks with no fee

[barakman]

This PR handles issue #601, with the following doubts remaining:

• Why are there rows in multichain_addresses.csv with no fee in them?
• Why is this issue relevant only for univ2 exchanges?
• There are other exchanges in this file with no fee defined for them; if this issue is relevant only for univ2, then why are there other exchanges for which there are some rows with fee and some rows without fee? Logically, it sounds like for each exchange, either the fee should be included in every row or omitted from every row

So that issue needs to be resolved from the cause root.
Either by removing lines with invalid data, or by updating them to consist of valid data.

This PR attempts to do so by removing lines with fork=univ2 and no fee.
But there are a few doubts remaining:

• Should these lines perhaps be instead updated to consist of valid data?
• Should other lines in this file be updated to consist of valid data?
• Should other lines in this file be removed?
• Should other lines in any other file be updated to consist of valid data?
• Should other lines in any other file be removed?