cardano-ledger-conformance: Remove CHANGELOG.md from cabal file

[erikd]

Currently empty.

Description

Without this file, this repository cannot be used as a source-package-repository because:

> cabal build all
HEAD is now at a62edfae6 CI: Add ghc-9.8.1 to the build matrix
Error: cabal: sdist of cardano-ledger-conformance-0.1.0.0: filepath wildcard
'CHANGELOG.md' does not match any files.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[lehins]

We should instead remove CHANGELOG.md from the cabal file, because this package will never be released, thus changelog makes little sense with absence of releasing and versioning

[lehins]

Thank you!