Gets rid of obsolete EntityWhitelist.IsValid() function (#28565)

Gets rid of obsolete IsValid function

Co-authored-by: plykiya <plykiya@protonmail.com>

Content.Shared/Whitelist/EntityWhitelist.cs

@@ -54,14 +54,4 @@ public sealed partial class EntityWhitelist
     /// </summary>
     [DataField]
     public bool RequireAll;
-
-    [Obsolete("Use WhitelistSystem")]
-    public bool IsValid(EntityUid uid, IEntityManager? man = null)
-    {
-        var sys = man?.System<EntityWhitelistSystem>() ??
-                  IoCManager.Resolve<IEntitySystemManager>().GetEntitySystem<EntityWhitelistSystem>();
-
-        return sys.IsValid(this, uid);
-
-    }
 }