Dont re-add the same source table

Fix #1309 : The call to AddTableSource(), which adds the table to
the manager, happens the first time when calling the base constructor
hence a explicit call to the same method is unnecessary and results
in exception being thrown

src/VisualStudio/Core/Def/Implementation/TableDataSource/MiscellaneousDiagnosticListTable.cs

@@ -22,7 +22,7 @@ internal class MiscellaneousDiagnosticListTable : VisualStudioBaseDiagnosticList
             SVsServiceProvider serviceProvider, MiscellaneousFilesWorkspace workspace, IDiagnosticService diagnosticService, ITableManagerProvider provider) :
             base(serviceProvider, workspace, diagnosticService, Identifier, provider)
         {
-            AddTableSource();
+            ConnectWorkspaceEvents();
         }
 
         /// this is for test only

src/VisualStudio/Core/Def/Implementation/TableDataSource/MiscellaneousTodoListTable.cs

@@ -20,7 +20,7 @@ internal class MiscellaneousTodoListTable : VisualStudioBaseTodoListTable
         public MiscellaneousTodoListTable(MiscellaneousFilesWorkspace workspace, ITodoListProvider todoListProvider, ITableManagerProvider provider) :
             base(workspace, todoListProvider, Identifier, provider)
         {
-            AddTableSource();
+            ConnectWorkspaceEvents();
         }
 
         // only for test