Remove ASTPrinter hack for inferred Failure type alias

Now that we're proactively renaming this typealias on creation, this
hack does nothing.

Author: DougGregor

lib/AST/ASTPrinter.cpp

@@ -5512,32 +5512,6 @@ void Decl::printInherited(ASTPrinter &Printer, const PrintOptions &Opts) const {
   printer.printInherited(this);
 }
 
-/// Determine whether this typealias is an inferred typealias "Failure" that
-/// would conflict with another entity named failure in the same type.
-static bool isConflictingFailureTypeWitness(
-    const TypeAliasDecl *typealias) {
-  if (!typealias->isImplicit())
-    return false;
-
-  ASTContext &ctx = typealias->getASTContext();
-  if (typealias->getName() != ctx.Id_Failure)
-    return false;
-
-  auto nominal = typealias->getDeclContext()->getSelfNominalTypeDecl();
-  if (!nominal)
-    return false;
-
-  // Look for another entity with the same name.
-  auto lookupResults = nominal->lookupDirect(
-      typealias->getName(), typealias->getLoc());
-  for (auto found : lookupResults) {
-    if (found != typealias)
-      return true;
-  }
-
-  return false;
-}
-
 bool Decl::shouldPrintInContext(const PrintOptions &PO) const {
   // Skip getters/setters. They are part of the variable or subscript.
   if (isa<AccessorDecl>(this))
@@ -5577,14 +5551,6 @@ bool Decl::shouldPrintInContext(const PrintOptions &PO) const {
     return PO.PrintIfConfig;
   }
 
-  // Prior to Swift 6, we shouldn't print the inferred associated type
-  // witness for AsyncSequence.Failure. It is always determined from the
-  // AsyncIteratorProtocol witness.
-  if (auto typealias = dyn_cast<TypeAliasDecl>(this)) {
-    if (isConflictingFailureTypeWitness(typealias))
-      return false;
-  }
-
   // Print everything else.
   return true;
 }