Alerting: Enable Unified Alerting for open source and enterprise (#49834)

This commit enables Unified Alerting for open source and enterprise unless disabled in configuration.

pkg/services/sqlstore/migrations/migrations.go

@@ -1,8 +1,6 @@
 package migrations
 
 import (
-	"os"
-
 	"github.com/grafana/grafana/pkg/services/featuremgmt"
 	"github.com/grafana/grafana/pkg/services/sqlstore/migrations/accesscontrol"
 	"github.com/grafana/grafana/pkg/services/sqlstore/migrations/ualert"
@@ -52,11 +50,6 @@ func (*OSSMigrations) AddMigration(mg *Migrator) {
 	addUserAuthTokenMigrations(mg)
 	addCacheMigration(mg)
 	addShortURLMigrations(mg)
-	// TODO Delete when unified alerting is enabled by default unconditionally (Grafana v9)
-	if err := ualert.CheckUnifiedAlertingEnabledByDefault(mg); err != nil { // this should always go before any other ualert migration
-		mg.Logger.Error("failed to determine the status of alerting engine. Enable either legacy or unified alerting explicitly and try again", "err", err)
-		os.Exit(1)
-	}
 	ualert.AddTablesMigrations(mg)
 	ualert.AddDashAlertMigration(mg)
 	addLibraryElementsMigrations(mg)