fix: clean up upstream reader abort listener (#1378)

Co-authored-by: Isaac Sanchez <isanchez-hawkins@arize.com>

packages/web/server/lib/event-stream/upstream-reader.test.js

@@ -234,7 +234,7 @@ describe('createUpstreamSseReader', () => {
     expect(attempt).toBe(2);
   });
 
-  it('removes reconnect delay abort listeners after normal timeout completion', async () => {
+  it('removes abort listeners after stop', async () => {
     const tracked = createTrackedSignal();
     let attempt = 0;
     let reader;
@@ -270,7 +270,6 @@ describe('createUpstreamSseReader', () => {
     await reader.start();
 
     expect(attempt).toBe(2);
-    // The top-level stop listener remains; the reconnect-delay listener should be removed.
-    expect(tracked.getListenerCount()).toBe(1);
+    expect(tracked.getListenerCount()).toBe(0);
   });
 });