Remove Razor diagnostic URI conversion workaround.

- Razor has implemented and inserted the "proper" handling of diagnostic URIs. Prior to this they would prefix file paths with a `/`. That's no longer true.
- Did not remove the entire method because it still has value in converting file paths into Uris and looks to be used by more than just the `InProcLnaguageServer` diagnostic path.

src/Features/LanguageServer/Protocol/Extensions/ProtocolConversions.cs

@@ -4,7 +4,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Runtime.InteropServices;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.DocumentHighlighting;
@@ -60,10 +59,6 @@ internal static class ProtocolConversions
             { WellKnownTags.NuGet, LSP.CompletionItemKind.Text }
         };
 
-        /// <summary>
-        /// Workaround for razor file paths being provided with a preceding slash on windows.
-        /// Long term fix in razor here - https://github.com/dotnet/aspnetcore/issues/19948
-        /// </summary>
         public static Uri GetUriFromFilePath(string filePath)
         {
             if (filePath is null)
@@ -71,12 +66,6 @@ public static Uri GetUriFromFilePath(string filePath)
                 throw new ArgumentNullException(nameof(filePath));
             }
 
-            // Remove preceding slash if we're on Window as it's an invalid URI.
-            if (filePath.StartsWith("/") && RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                filePath = filePath.Substring(1);
-            }
-
             return new Uri(filePath, UriKind.Absolute);
         }