remove GADT syntax from existential wrappers (#49)

src/Simplex/Messaging/Agent/Transmission.hs

@@ -68,8 +68,7 @@ instance TestEquality SAParty where
   testEquality SClient SClient = Just Refl
   testEquality _ _ = Nothing
 
-data ACmd where
-  ACmd :: SAParty p -> ACommand p -> ACmd
+data ACmd = forall p. ACmd (SAParty p) (ACommand p)
 
 deriving instance Show ACmd
 

src/Simplex/Messaging/Protocol.hs

@@ -41,8 +41,7 @@ data SParty :: Party -> Type where
 
 deriving instance Show (SParty a)
 
-data Cmd where
-  Cmd :: SParty a -> Command a -> Cmd
+data Cmd = forall a. Cmd (SParty a) (Command a)
 
 deriving instance Show Cmd