Remove ShelleyMode and ByronMode

[newhoggy]

Changelog

- description: |
    Remove `ShelleyMode` and `ByronMode`
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - improvement    # QoL changes e.g. refactoring
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

We no longer use ShelleyMode and ByronMode and they can be removed.

The removal of these modes results in significant simplification of the CLI codebase.

These modes still exist in cardano-api. They are removed in cardano-node first to minimise dependency risk.

How to trust this PR

Highlight important bits of the PR that will make the review faster. If there are commands the reviewer can run to observe the new behavior, describe them.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[Jimbo4350]

LGTM!

[Jimbo4350]

💪

[mkoura]

Regression tests passed ✔️