AST: Adopt AvailableAttr::isLanguageVersionSpecific().

Author: tshortli

lib/AST/Attr.cpp

@@ -379,8 +379,7 @@ DeclAttributes::isUnavailableInSwiftVersion(
       if (available->isInvalid())
         continue;
 
-      if (available->getPlatformAgnosticAvailability() ==
-          PlatformAgnosticAvailabilityKind::SwiftVersionSpecific) {
+      if (available->isLanguageVersionSpecific()) {
         if (available->Introduced.has_value() &&
             available->Introduced.value() > vers)
           return true;

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -916,8 +916,7 @@ CheckRedeclarationRequest::evaluate(Evaluator &eval, ValueDecl *current,
           static AvailabilityRange from(const ValueDecl *VD) {
             AvailabilityRange result;
             for (auto *attr : VD->getAttrs().getAttributes<AvailableAttr>()) {
-              if (attr->getPlatformAgnosticAvailability() ==
-                  PlatformAgnosticAvailabilityKind::SwiftVersionSpecific) {
+              if (attr->isLanguageVersionSpecific()) {
                 if (attr->Introduced)
                   result.introduced = attr->Introduced;
                 if (attr->Obsoleted)