remove unused method declaration

src/compiler/types.ts

@@ -2908,7 +2908,6 @@ namespace ts {
         getCancellationToken?(): CancellationToken;
         getDefaultLibFileName(options: CompilerOptions): string;
         getDefaultLibLocation?(): string;
-        getDefaultTypeDirectiveNames?(rootPath: string): string[];
         writeFile: WriteFileCallback;
         getCurrentDirectory(): string;
         getDirectories(path: string): string[];