Deduplicate the era case in readFileSimpleScript

Decode the JSON SimpleScript once and convert it to a Conway timelock
before the era case, so each era branch is a single expression; this
drops the obtainConwayConstraints wrapper and the TypeApplications
pragma. Suggested by the review of #1427.

Author: palas

cardano-cli/src/Cardano/CLI/EraBased/Script/Read/Common.hs

@@ -2,7 +2,6 @@
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE TypeApplications #-}
 
 module Cardano.CLI.EraBased.Script.Read.Common
   ( -- * Plutus Script Related
@@ -40,20 +39,16 @@ readFileSimpleScript
 readFileSimpleScript file era = do
   bs <- readFileCli file
   case deserialiseFromJSON bs of
-    Left _ -> case era of
-      Exp.DijkstraEra -> Exp.obtainCommonConstraints era $ do
-        -- In addition to the TextEnvelope format, we also try to
-        -- deserialize the JSON representation of SimpleScripts.
-        script :: SimpleScript <- fromEitherCli $ Aeson.eitherDecodeStrict' bs
-        let s :: L.NativeScript (Exp.LedgerEra era) =
-              Dijkstra.upgradeTimelock (toAllegraTimelock @(Exp.LedgerEra Exp.ConwayEra) script)
-        return $ Exp.SimpleScript s
-      Exp.ConwayEra -> Exp.obtainConwayConstraints era $ do
-        -- In addition to the TextEnvelope format, we also try to
-        -- deserialize the JSON representation of SimpleScripts.
-        script :: SimpleScript <- fromEitherCli $ Aeson.eitherDecodeStrict' bs
-        let s :: L.NativeScript (Exp.LedgerEra era) = obtainCommonConstraints era $ toAllegraTimelock script
-        return $ Exp.SimpleScript s
+    Left _ -> do
+      -- In addition to the TextEnvelope format, we also try to
+      -- deserialize the JSON representation of SimpleScripts.
+      script :: SimpleScript <- fromEitherCli $ Aeson.eitherDecodeStrict' bs
+      let conwayTimelock :: L.NativeScript (Exp.LedgerEra Exp.ConwayEra)
+          conwayTimelock = toAllegraTimelock script
+      Exp.obtainCommonConstraints era $
+        pure . Exp.SimpleScript $ case era of
+          Exp.DijkstraEra -> Dijkstra.upgradeTimelock conwayTimelock
+          Exp.ConwayEra -> conwayTimelock
     Right te -> do
       let scriptBs = teRawCBOR te
       obtainCommonConstraints era $