test: simplify restoring /var/lib/sudo/lectured

Use restore_dir instead of restoring four different files.

test/verify/check-superuser

@@ -65,14 +65,11 @@ class TestSuperuser(testlib.MachineCase):
         b.drop_superuser()
 
         # We want to be lectured again
-        self.restore_file("/var/db/sudo/lectured/admin")
-        self.restore_file("/var/lib/sudo/lectured/admin")
-        m.execute("rm -rf /var/{db,lib}/sudo/lectured/admin")
+        self.restore_dir("/var/db/sudo/lectured")
 
+        m.execute("rm -rf /var/{db,lib}/sudo/lectured/admin")
         # Sudo since 1.9.15 uses a UID not a username https://www.sudo.ws/releases/stable/#1.9.15
         uid = m.execute("id -u admin").strip()
-        self.restore_file(f"/var/db/sudo/lectured/{uid}")
-        self.restore_file(f"/var/lib/sudo/lectured/{uid}")
         m.execute(f"rm -rf /var/{{db,lib}}/sudo/lectured/{uid}")
 
         # Get the privileges back, this time in the mobile layout