Remove unused usings of namespaces .NET doesn't have System.Media, System.Runtime.Remoting.Messaging, System.Security.Policy and System.Net.Configuration are .NET Framework namespaces that Mono's profile carries and .NET doesn't, so these eight files stop compiling under CoreCLR. Nothing in them uses the namespaces, so the lines just go; a using can only bind names, so if one had been needed the file would fail to compile rather than change meaning. Hand-ported from unity_6.7.0's changeset 169906 (ab1e999ad3c, "Fix some more serialisation issues that came up when switching to CoreCLR"), whose using removals apply to main as they are; its serialisation attributes are the next commit. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>