Fix logic to determine whether an app is a system app

Checking the path is not reliable since %WINDIR% can be
"C:\WINDOWS" instead of "C:\Windows" on some systems

src/Utils/AppxRemover.cs

@@ -48,8 +48,7 @@ private Result PerformAppsRemoval(string[] appNames, RemovalMethod removalMethod
 
     private static bool IsSystemApp(Package package)
     {
-        string systemAppsFolder = $@"{Environment.GetFolderPath(Environment.SpecialFolder.Windows)}\SystemApps";
-        return package.InstalledPath.StartsWith(systemAppsFolder);
+        return package.SignatureKind == PackageSignatureKind.System;
     }
 
     private abstract class RemovalMethod