Remove unneeded ArgumentNullException

Author: DustinCampbell

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/ProjectSystem/SnapshotResolver.cs

@@ -47,11 +47,6 @@ public Task InitializeAsync(CancellationToken cancellationToken)
     /// <inheritdoc/>
     public ImmutableArray<IProjectSnapshot> FindPotentialProjects(string documentFilePath)
     {
-        if (documentFilePath is null)
-        {
-            throw new ArgumentNullException(nameof(documentFilePath));
-        }
-
         var normalizedDocumentPath = FilePathNormalizer.Normalize(documentFilePath);
 
         using var projects = new PooledArrayBuilder<IProjectSnapshot>();