Alerting: remove feature toggle for provisioning API (#50167) (#50213)

* Alerting: remove feature toggle for provisioning API

* remove missed code parts

* remove unused import

* remove empty line

* mark routes as stable

(cherry picked from commit 4b8a4449ed)

Co-authored-by: Jean-Philippe Quéméner <JohnnyQQQQ@users.noreply.github.com>

pkg/tests/api/alerting/api_provisioning_test.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/grafana/grafana/pkg/infra/tracing"
 	"github.com/grafana/grafana/pkg/models"
-	"github.com/grafana/grafana/pkg/services/featuremgmt"
 	"github.com/grafana/grafana/pkg/tests/testinfra"
 	"github.com/stretchr/testify/require"
 )
@@ -23,7 +22,6 @@ func TestProvisioning(t *testing.T) {
 		EnableUnifiedAlerting: true,
 		DisableAnonymous:      true,
 		AppModeProduction:     true,
-		EnableFeatureToggles:  []string{featuremgmt.FlagAlertProvisioning},
 	})
 
 	grafanaListedAddr, store := testinfra.StartGrafana(t, dir, path)