ref(node): Remove vendored Koa instrumentation (#22751)

## What

Removes the dead OpenTelemetry `KoaInstrumentation` (and
`instrumentKoa`) plus its vendored code from `@sentry/node`. Keeps
`setupKoaErrorHandler`.

## Why

The Koa integration is now provided by the channel-based implementation
in `@sentry/server-utils` (the default since #22501). The vendored
instrumentation is no longer wired up; only the Sentry-specific error
handler remains user-facing.

Ref: #22346

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: andreiborza

packages/node/src/integrations/tracing/koa/index.ts

@@ -1,28 +1,6 @@
-import type { KoaInstrumentationConfig, KoaLayerType } from './vendored/types';
-import { KoaInstrumentation } from './vendored/instrumentation';
 import { captureException } from '@sentry/core';
-import { generateInstrumentOnce } from '../../../otel/instrument';
 import { ensureIsWrapped } from '../../../utils/ensureIsWrapped';
 
-interface KoaOptions {
-  /**
-   * Ignore layers of specified types
-   */
-  ignoreLayersType?: Array<'middleware' | 'router'>;
-}
-
-const INTEGRATION_NAME = 'Koa' as const;
-
-export const instrumentKoa = generateInstrumentOnce(
-  INTEGRATION_NAME,
-  KoaInstrumentation,
-  (options: KoaOptions = {}) => {
-    return {
-      ignoreLayersType: options.ignoreLayersType as KoaLayerType[],
-    } satisfies KoaInstrumentationConfig;
-  },
-);
-
 /**
  * Add an Koa error handler to capture errors to Sentry.
  *