docs(dev-docs): Remove alert for metrics (#15506)

Author: chargome

develop-docs/sdk/telemetry/metrics.mdx

@@ -3,12 +3,6 @@ title: Metrics
 sidebar_order: 4
 ---
 
-<Alert title="Note" level="warning">
-
-The Sentry Metrics feature is under active development. The information in this document is subject to change.
-
-</Alert>
-
 This document defines the format used by Sentry to ingest metrics, as well as the SDK API and behavior that create and send metrics to Sentry.
 
 <Alert title="Note" level="info">