Remove ConwayPool rule definition

[lehins]

Description

Conway's POOL is identical to the one in Shelley. There is no need to redefine it.

This PR removes ConwayPool in favor of ShelleyPOOL

It also:

• Removes usage of ShelleyTx in Shelley and Allegra rules in favor of Tx type family
• Makes EraRule rule era invective in the rule. This will help avoid mistakes like this:

type instance EraRule "UTXOW" (ConwayEra c) = ConwayUTXOW (ConwayEra c)
type instance EraRule "UTXOS" (ConwayEra c) = ConwayUTXOW (ConwayEra c)

Unfortunately it can't be made injective in era as well, because of TICKN:

cardano-ledger/eras/shelley-ma/test-suite/test/Tests.hs

Lines 34 to 36 in 0e65b5e

	type instance EraRule "TICKN" (MaryEra _c) = TPraos.TICKN
	type instance EraRule "TICKN" (AllegraEra _c) = TPraos.TICKN

Maybe in the future will be able to solve that one, which will help with type inference

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

[aniketd]

LGTM 👍 Thank you!