B: Get rid of Params().RequireStandard() #16527

Based on #16524 Alternative to #16526

This goes further and just like in #16524 it removes the different defaults for each chain.

In my opinion, one thing is to want to prevent people from shooting themselves in the food like AllowAcceptNonstd()/IsTestChain() allows for mainnet and a very different one is having per chain defaults for each parameter.

testnet3 and regtest users will now need to modify their config files, at most, in the following way:

[main]
+acceptnonstdtxn=0
...

[test]
+acceptnonstdtxn=1
...

[regtest]
+acceptnonstdtxn=0
...

I don't think that's much to ask from the advanced users regtest and testnet users are supposed to be. Maybe this is different for testnet3, I would like to hear why.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #17037 (Testschains: Many regtests with different genesis and default datadir by jtimon)
• #17032 (Tests: Chainparams: Make regtest almost fully customizable by jtimon)
• #16770 (Chainparams: Rename IsTestChain() to AllowAcceptNonstd() by jtimon)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

Rebased

Decoupled from #16524

This means that non std txs aren't propagated on testnet, so tend to NACK

Well, only if users don't set acceptnonstdtxn=1, we could say it in the release notes. But yeah, that's, I think, the best argument against this.

It makes sense to default to -acceptnonstdtxn=1 on testnet. But it's also just testnet, so don't care too strongly.

Closing for now due to lack of interest.