http: free listeners on free sockets

Reduced memory usage by ensuring free sockets don't have extra
listeners while in the pool.

lib/_http_client.js

@@ -601,6 +601,8 @@ function responseKeepAlive(req) {
   }
   socket.removeListener('close', socketCloseListener);
   socket.removeListener('error', socketErrorListener);
+  socket.removeListener('data', socketOnData);
+  socket.removeListener('end', socketOnEnd);
   socket.once('error', freeSocketErrorListener);
   // There are cases where _handle === null. Avoid those. Passing null to
   // nextTick() will call getDefaultTriggerAsyncId() to retrieve the id.

test/parallel/test-http-agent-keepalive.js

@@ -137,9 +137,19 @@ server.listen(0, common.mustCall(() => {
 
 // Check for listener leaks when reusing sockets.
 function checkListeners(socket) {
-  assert.strictEqual(socket.listenerCount('data'), 1);
-  assert.strictEqual(socket.listenerCount('drain'), 1);
-  assert.strictEqual(socket.listenerCount('error'), 1);
-  // Sockets have onReadableStreamEnd.
-  assert.strictEqual(socket.listenerCount('end'), 2);
+  const callback = common.mustCall(() => {
+    if (!socket.destroyed) {
+      assert.strictEqual(socket.listenerCount('data'), 0);
+      assert.strictEqual(socket.listenerCount('drain'), 0);
+      // Sockets have freeSocketErrorListener.
+      assert.strictEqual(socket.listenerCount('error'), 1);
+      // Sockets have onReadableStreamEnd.
+      assert.strictEqual(socket.listenerCount('end'), 1);
+    }
+
+    socket.off('free', callback);
+    socket.off('close', callback);
+  });
+  socket.once('free', callback);
+  socket.once('close', callback);
 }