chore(cockpit): remove expert plan (#2025)

Author: scaleway-bot

api/cockpit/v1beta1/cockpit_sdk.go

@@ -269,9 +269,8 @@ const (
 PlanNameFree = PlanName("free")
 // The premium plan with a longer retention.
 PlanNamePremium = PlanName("premium")
-PlanNameCustom = PlanName("custom")
-// The expert plan with the longest retention.
-PlanNameExpert = PlanName("expert")
+// The custom plan.
+PlanNameCustom = PlanName("custom")
 )
 
 func (enum PlanName) String() string {