Tidy: drop Ledger.Era era => constraint from Tx pattern

It is unnecessary.

It should also never have been there in the first place since doing so
exposes things from the underlying libraries that the API is trying to
wrap and hide.

cardano-api/src/Cardano/Api/Tx.hs

@@ -394,7 +394,7 @@ instance IsCardanoEra era => HasTextEnvelope (KeyWitness era) where
         AlonzoEra  -> "TxWitness AlonzoEra"
 
 
-pattern Tx :: Ledger.Era era => TxBody era -> [KeyWitness era] -> Tx era
+pattern Tx :: TxBody era -> [KeyWitness era] -> Tx era
 pattern Tx txbody ws <- (getTxBodyAndWitnesses -> (txbody, ws))
   where
     Tx txbody ws = makeSignedTransaction ws txbody