[FixCode] Protocol stubs shouldn't print any @ attributes.

This also addresses @jrose-apple's code review comments.

Author: nkcsgexi

lib/Sema/TypeCheckProtocol.cpp

@@ -2654,7 +2654,7 @@ printRequirementStub(ValueDecl *Requirement, DeclContext *Adopter,
     Options.PrintDocumentationComments = false;
     Options.AccessibilityFilter = Accessibility::Private;
     Options.PrintAccessibility = false;
-    Options.ExcludeAttrList.push_back(DAK_Available);
+    Options.SkipAttributes = true;
     Options.FunctionBody = [](const ValueDecl *VD) { return getCodePlaceholder(); };
     Options.setBaseType(AdopterTy);
     Options.CurrentModule = Adopter->getParentModule();

test/decl/protocol/conforms/fixit_stub_editor.swift

@@ -1,7 +1,7 @@
 // RUN: %target-typecheck-verify-swift -diagnostics-editor-mode
 
 protocol P1 {
-  @available(*, introduced: 999)
+  @available(*, deprecated)
   func foo1()
   func foo2()
 }