remove: drop support for PostgreSQL 12

This has been EOL since November and has been dropped from nixpkgs.

src/PostgREST/SchemaCache/Routine.hs

@@ -14,7 +14,6 @@ module PostgREST.SchemaCache.Routine
   , funcReturnsSingleComposite
   , funcReturnsVoid
   , funcTableName
-  , funcReturnsCompositeAlias
   , funcReturnsSingle
   , MediaHandlerMap
   , ResolvedHandler
@@ -127,12 +126,6 @@ funcReturnsSetOfScalar proc = case proc of
   Function{pdReturnType = SetOf (Scalar{})} -> True
   _                                         -> False
 
-funcReturnsCompositeAlias :: Routine -> Bool
-funcReturnsCompositeAlias proc = case proc of
-  Function{pdReturnType = Single (Composite _ True)} -> True
-  Function{pdReturnType = SetOf (Composite _ True)}  -> True
-  _                                                  -> False
-
 funcReturnsSingleComposite :: Routine -> Bool
 funcReturnsSingleComposite proc = case proc of
   Function{pdReturnType = Single (Composite _ _)} -> True