Update deprecation notice for legacy alerts API

Removed the removal date for the legacy alerts API.

Author: EdB-MSFT

api-reference/v1.0/includes/security-alerts-v1-deprecation.md

@@ -7,4 +7,4 @@ ms.topic: include
 
 <!-- markdownlint-disable MD041-->
 > [!NOTE]
-> The legacy alerts API is deprecated and will be removed by April 2026. We recommend that you migrate to the new [alerts and incidents](/graph/api/resources/security-alert) API.
+> The legacy alerts API is deprecated. We recommend that you migrate to the new [alerts and incidents](/graph/api/resources/security-alert) API.