Remove ByronTx

[Jimbo4350]

Changelog

- description: |
    Remove `ByronTx` data constructor from `data Tx era`
    Delete Cardano.Api.Eon.ByronEraOnly module
    Remove `TxFeeImplicit` and `TxValidityNoUpperBound`
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[Jimbo4350]

We actually do if QA intends to use foldBlocks with their hard forking tests. Not strictly true as foldBlocks can be called when we enter the Shelley era. It does not make sense to call foldBlocks in Byron because Byron does not have ledger events.

[carlhammann]

Looks good to me!