Remove #nullable enable

Jellyfin.Api/Auth/BaseAuthorizationHandler.cs

@@ -1,6 +1,4 @@
-#nullable enable
-
-using System.Net;
+using System.Net;
 using System.Security.Claims;
 using Jellyfin.Api.Helpers;
 using Jellyfin.Data.Enums;

Jellyfin.Api/Auth/CustomAuthenticationHandler.cs

@@ -1,5 +1,3 @@
-#nullable enable
-
 using System.Globalization;
 using System.Security.Authentication;
 using System.Security.Claims;

Jellyfin.Api/Helpers/ClaimHelpers.cs

@@ -1,6 +1,4 @@
-#nullable enable
-
-using System;
+using System;
 using System.Linq;
 using System.Security.Claims;
 using Jellyfin.Api.Constants;