[NFC] Remove ModuleDecl::isClangModule in favor of isNonSwiftModule. (#33202)

Fixes SR-13237.

Author: mateioprea

include/swift/AST/Module.h

@@ -367,7 +367,6 @@ class ModuleDecl : public DeclContext, public TypeDecl {
     return { Files.begin(), Files.size() };
   }
 
-  bool isClangModule() const;
   void addFile(FileUnit &newFile);
 
   /// Creates a map from \c #filePath strings to corresponding \c #fileID

lib/AST/Module.cpp

@@ -493,9 +493,6 @@ ArrayRef<ImplicitImport> ModuleDecl::getImplicitImports() const {
                            {});
 }
 
-bool ModuleDecl::isClangModule() const {
-  return findUnderlyingClangModule() != nullptr;
-}
 
 void ModuleDecl::addFile(FileUnit &newFile) {
   // If this is a LoadedFile, make sure it loaded without error.

lib/Index/IndexSymbol.cpp

@@ -143,7 +143,7 @@ SymbolInfo index::getSymbolInfoForModule(ModuleEntity Mod) {
   info.SubKind = SymbolSubKind::None;
   info.Properties = SymbolPropertySet();
   if (auto *D = Mod.getAsSwiftModule()) {
-    if (!D->isClangModule()) {
+    if (!D->isNonSwiftModule()) {
       info.Lang = SymbolLanguage::Swift;
     } else {
       info.Lang = SymbolLanguage::C;

tools/swift-ide-test/swift-ide-test.cpp

@@ -3191,7 +3191,7 @@ static int doPrintModuleImports(const CompilerInvocation &InitInvok,
     SmallVector<ModuleDecl::ImportedModule, 16> scratch;
     for (auto next : namelookup::getAllImports(M)) {
       llvm::outs() << next.importedModule->getName();
-      if (next.importedModule->isClangModule())
+      if (next.importedModule->isNonSwiftModule())
         llvm::outs() << " (Clang)";
       llvm::outs() << ":\n";
 
@@ -3205,7 +3205,7 @@ static int doPrintModuleImports(const CompilerInvocation &InitInvok,
           llvm::outs() << "." << accessPathPiece.Item;
         }
 
-        if (import.importedModule->isClangModule())
+        if (import.importedModule->isNonSwiftModule())
           llvm::outs() << " (Clang)";
         llvm::outs() << "\n";
       }