Switch to higher level XPC & enforce signing requirements (#681)

* Revert "Add launch constraints (#678)"

This reverts commit c5a610d786.

* .

* Cleanup.

Sources/SecretiveUpdater/main.swift

@@ -0,0 +1,7 @@
+import Foundation
+import XPCWrappers
+
+let delegate = XPCServiceDelegate(exportedObject: SecretiveUpdater())
+let listener = NSXPCListener.service()
+listener.delegate = delegate
+listener.resume()