revert(server): drop the licence grandfather migration

Instances stay read-only until a licence is set. No licence is generated by
the control plane, which keeps the signing key out of it entirely.

server/cmd/main.go

@@ -59,13 +59,6 @@ func main() {
 		log.Fatalf("scoped collection check failed: %v", assertErr)
 	}
 
-	gfCtx, gfCancel := context.WithTimeout(context.Background(), 2*time.Minute)
-	gfErr := services.MigrateGrandfatherLicences(gfCtx, db.Database)
-	gfCancel()
-	if gfErr != nil {
-		log.Fatalf("licence grandfather migration failed: %v", gfErr)
-	}
-
 	if err := services.EnsureAuthIndexes(); err != nil {
 		log.Fatalf("failed to ensure auth indexes: %v", err)
 	}