Revert "Call AdviseRunningDocTableEvents on UI thread. (#5783)" (#5832)

This reverts commit 1f785f416c.

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/Documents/VisualStudioEditorDocumentManager.cs

@@ -52,14 +52,8 @@ namespace Microsoft.VisualStudio.Editor.Razor.Documents
             _runningDocumentTable = (IVsRunningDocumentTable4)runningDocumentTable;
             _editorAdaptersFactory = editorAdaptersFactory;
 
-            // Need to grab running doc-table events but that requires the UI thread.
-            joinableTaskContext.Factory.Run(async () =>
-            {
-                await joinableTaskContext.Factory.SwitchToMainThreadAsync();
-
-                var hr = runningDocumentTable.AdviseRunningDocTableEvents(new RunningDocumentTableEventSink(this), out _);
-                Marshal.ThrowExceptionForHR(hr);
-            });
+            var hr = runningDocumentTable.AdviseRunningDocTableEvents(new RunningDocumentTableEventSink(this), out _);
+            Marshal.ThrowExceptionForHR(hr);
 
             _documentsByCookie = new Dictionary<uint, List<DocumentKey>>();
             _cookiesByDocument = new Dictionary<DocumentKey, uint>();