Remove no longer needed workarounds

[lehins]

Description

This PR removes conditional decoding workarounds that where set in place in order to preserve the behavior of decoders, until we are in newer eras where fix is permanent:

• Removes the IgnoreSigOrd, which, until Alonzo, preserved the behavior of older Ord instance for WitVKey. Fixes Attempt removing IgnoreSigOrd #4902
• Remove conditional decoding for Coin, which until Conway era allowed negative coin in a couple of obscure places.
• Adds a comment about inability to remove buggy translation of certificated in plutus context for protocol version 9. Fixes Attempt removing conditional translation of certificates #4863

This change has been verified to have no affect on mainnet, preview and preprod. Therefore removal of those hacks can now be safely removed.

Checklist

• Commits in meaningful sequence and with useful messages
• Tests added or updated when needed
• CHANGELOG.md files updated for packages with externally visible changes
  
  New section is never added with the code changes. (See RELEASING.md)
• Versions updated in .cabal and CHANGELOG.md files when necessary, according to the
  versioning process.
• Version bounds in .cabal files updated when necessary
  
  If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• Code formatted (use scripts/fourmolize.sh)
• Cabal files formatted (use scripts/cabal-format.sh)
• hie.yaml updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[teodanciu]

Looks good to me, thanks for explaining and linking to why they are not needed anymore 👍

A CBOR roundtrip test is failing, as it's not longer true that " Negative Coin succeeds for pre-Conway`, so we could probably just remove it : https://github.com/IntersectMBO/cardano-ledger/blob/lehins/remove-no-longer-needed-hacks/eras/mary/impl/test/Test/Cardano/Ledger/Mary/ValueSpec.hs#L50

[lehins]

A CBOR roundtrip test is failing, as it's not longer true that " Negative Coin succeeds for pre-Conway`, so we could probably just remove it

Yep. Removed it.