Abandoned using ReadOnlyDocument: Revert

src/Libraries/NewNRefactory/ICSharpCode.NRefactory/Editor/ReadOnlyDocument.cs

@@ -25,7 +25,7 @@ namespace ICSharpCode.NRefactory.Editor
 	/// Read-only implementation of <see cref="IDocument"/>.
 	/// </summary>
 	[Serializable]
-	public sealed class ReadOnlyDocument : IDocument
+	sealed class ReadOnlyDocument : IDocument
 	{
 		readonly ITextSource textSource;
 		int[] lines;