Small items for code review iteration

* Removing unused OutputType and OutputWrittenEventArgs classes
* Adding class comment blocks
* Tweaking a couple comment blocks as per @kcunanne comments

src/ServiceHost/LanguageServices/LanguageService.cs

@@ -18,7 +18,8 @@ using System.Linq;
 namespace Microsoft.SqlTools.ServiceLayer.LanguageServices
 {
     /// <summary>
-    /// Main class for Language Service functionality
+    /// Main class for Language Service functionality including anything that reqires knowledge of
+    /// the language to perfom, such as definitions, intellisense, etc.
     /// </summary>
     public sealed class LanguageService
     {