ASTPrinter: Remove opaque archetype re-sugaring hack

We cannot in general assume the substitution map's replacement types
are written in terms of the generic signautre of the owner declaration.

This was only necessary because this substitution map did not
preserve type sugar, but now that it does, we no longer need
this hack.

Author: slavapestov

lib/AST/ASTPrinter.cpp

@@ -3634,16 +3634,6 @@ void PrintAST::visitTypeAliasDecl(TypeAliasDecl *decl) {
 
   if (ShouldPrint) {
     Printer << " = ";
-    // FIXME: An inferred associated type witness type alias may reference
-    // an opaque type, but OpaqueTypeArchetypes are always canonicalized
-    // so lose type sugar for generic params. Bind the generic signature so
-    // we can map params back into the generic signature and print them
-    // correctly.
-    //
-    // Remove this when we have a way to represent non-canonical archetypes
-    // preserving sugar.
-    PrintOptions::OverrideScope scope(Options);
-    OVERRIDE_PRINT_OPTION(scope, GenericSig, decl->getGenericSignature().getPointer());
     printTypeLoc(TypeLoc(decl->getUnderlyingTypeRepr(), Ty));
     printDeclGenericRequirements(decl);
   }
@@ -7500,11 +7490,6 @@ class TypePrinter : public TypeVisitor<TypePrinter, void, NonRecursivePrintOptio
       if (auto existential = constraint->getAs<ExistentialType>())
         constraint = existential->getConstraintType();
 
-      // Opaque archetype substitutions are always canonical, so re-sugar the
-      // constraint type using the owning declaration's generic parameter names.
-      if (genericSig)
-        constraint = genericSig->getSugaredType(constraint);
-
       visit(constraint);
       return;
     }