Deprecate TxVotesSupportedInEra

[newhoggy]

Changelog

- description: |
    Deprecate `TxVotesSupportedInEra`
  compatibility: breaking
  type: feature

Context

TxVotesSupportedInEra and ConwayEraOnwards are near identical.

Using ConwayEraOnwards everywhere instead.

The deprecation and switch to ConwayEraOnwards serves the following purpose:

• Reduce the size of the API
• Documentation that a type, constructor or function only works from Conway era onwards. Use of TxVotesSupportedInEra did not make this clear
• Reduce the amount of glue code required for different parts of the CLI to work together.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• The change log section in the PR description has been filled in
• New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • roundtrip tests
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
  • Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • Code builds on Linux, MacOS and Windows for ghc-8.10.7 and ghc-9.2.7
• The changelog section in the PR is updated to describe the change
• Self-reviewed the diff

Note on CI

If your PR is from a fork, the necessary CI jobs won't trigger automatically for security reasons.
You will need to get someone with write privileges. Please contact IOG node developers to do this
for you.

[Jimbo4350]

So this assumes that we will always have voting in the Conway era onwards, which is a reasonable assumption.