Abstract getWitsVKeyNeeded

[lehins]

Description

Turns out GenDelegs is totally unnecessary in the UtxoEnv. This PR removes it.

Also it adds an era agnostic getWitsVKeyNeeded that we can now use in UTXOW rules for all eras.

This is a nice organization and simplification, but the real reason for this change is that we need to provide a proper min fee computation for CLI, which will be implemented in a subsequent PR

Fixes #3485

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

[teodanciu]

Looks good to me.
Love how the second commit cleans up so much noise, awesome.