Mark email transport webhook endpoint as private (#36618)

Co-authored-by: ci.datadog-api-spec <packages@datadoghq.com>

Author: api-clients-generation-pipeline[bot]

config/_default/menus/api.en.yaml

@@ -9188,23 +9188,6 @@ menu:
           - GetDomainAllowlist
         unstable: []
         order: 1
-    - name: Email Transport
-      url: /api/latest/email-transport/
-      identifier: email-transport
-      generated: true
-    - name: Ingest email transport webhook events
-      url: '#ingest-email-transport-webhook-events'
-      identifier: email-transport-ingest-email-transport-webhook-events
-      parent: email-transport
-      generated: true
-      params:
-        versions:
-          - v2
-        operationids:
-          - CreateEmailTransportWebhookIntake
-        unstable:
-          - v2
-        order: 1
     - name: Entity Risk Scores
       url: /api/latest/entity-risk-scores/
       identifier: entity-risk-scores