Sema: Retire some ExportContext availability conveniences.

Just use the `AvailabilityContext` directly.

Author: tshortli

lib/Sema/TypeCheckAvailability.cpp

@@ -1488,18 +1488,19 @@ static void diagnoseIfDeprecated(SourceRange ReferenceRange,
   if (!Attr)
     return;
 
+  auto Availability = Where.getAvailability();
+
   // We match the behavior of clang to not report deprecation warnings
   // inside declarations that are themselves deprecated on all deployment
   // targets.
-  if (Where.isDeprecated()) {
+  if (Availability.isDeprecated()) {
     return;
   }
 
   auto *ReferenceDC = Where.getDeclContext();
   auto &Context = ReferenceDC->getASTContext();
   if (!Context.LangOpts.DisableAvailabilityChecking) {
-    AvailabilityRange RunningOSVersions = Where.getAvailabilityRange();
-    if (RunningOSVersions.isKnownUnreachable()) {
+    if (Availability.getPlatformRange().isKnownUnreachable()) {
       // Suppress a deprecation warning if the availability checking machinery
       // thinks the reference program location will not execute on any
       // deployment target for the current platform.
@@ -1567,18 +1568,19 @@ static bool diagnoseIfDeprecated(SourceLoc loc,
   if (!attr)
     return false;
 
+  auto availability = where.getAvailability();
+
   // We match the behavior of clang to not report deprecation warnings
   // inside declarations that are themselves deprecated on all deployment
   // targets.
-  if (where.isDeprecated()) {
+  if (availability.isDeprecated()) {
     return false;
   }
 
   auto *dc = where.getDeclContext();
   auto &ctx = dc->getASTContext();
   if (!ctx.LangOpts.DisableAvailabilityChecking) {
-    AvailabilityRange runningOSVersion = where.getAvailabilityRange();
-    if (runningOSVersion.isKnownUnreachable()) {
+    if (availability.getPlatformRange().isKnownUnreachable()) {
       // Suppress a deprecation warning if the availability checking machinery
       // thinks the reference program location will not execute on any
       // deployment target for the current platform.

lib/Sema/TypeCheckAvailability.h

@@ -164,10 +164,6 @@ class ExportContext {
 
   AvailabilityContext getAvailability() const { return Availability; }
 
-  AvailabilityRange getAvailabilityRange() const {
-    return Availability.getPlatformRange();
-  }
-
   /// If not 'None', the context has the inlinable function body restriction.
   FragileFunctionKind getFragileFunctionKind() const { return FragileKind; }
 
@@ -188,10 +184,6 @@ class ExportContext {
   /// or declarations from `@_implementationOnly` imports.
   bool isExported() const { return Exported; }
 
-  /// If true, the context is part of a deprecated declaration and can
-  /// reference other deprecated declarations without warning.
-  bool isDeprecated() const { return Availability.isDeprecated(); }
-
   /// If true, the context can only reference exported declarations, either
   /// because it is the signature context of an exported declaration, or
   /// because it is the function body context of an inlinable function.

lib/Sema/TypeCheckProtocol.cpp

@@ -1904,7 +1904,7 @@ RequirementCheck WitnessChecker::checkWitness(ValueDecl *requirement,
     isDefaultWitness = isa<ProtocolDecl>(nominal);
   if (isDefaultWitness && match.Witness->isDeprecated() &&
       !requirement->isDeprecated()) {
-    auto conformanceContext = ExportContext::forConformance(DC, Proto);
+    auto conformanceContext = AvailabilityContext::forDeclSignature(DC->getInnermostDeclarationDeclContext());
     if (!conformanceContext.isDeprecated()) {
       return RequirementCheck(CheckKind::DefaultWitnessDeprecated);
     }