feat(alerting): removed old init package

pkg/services/alerting/init/init.go

-package init
-
-import (
-	"context"
-
-	"github.com/grafana/grafana/pkg/services/alerting"
-	_ "github.com/grafana/grafana/pkg/services/alerting/conditions"
-	_ "github.com/grafana/grafana/pkg/services/alerting/notifiers"
-	"github.com/grafana/grafana/pkg/setting"
-	_ "github.com/grafana/grafana/pkg/tsdb/graphite"
-	_ "github.com/grafana/grafana/pkg/tsdb/prometheus"
-	_ "github.com/grafana/grafana/pkg/tsdb/testdata"
-)
-
-func Init(ctx context.Context) error {
-	if !setting.AlertingEnabled {
-		return nil
-	}
-
-	engine = alerting.NewEngine()
-	return engine.Start(ctx)
-}