Stub out ios_on_send_window_available

Signed-off-by: JP Simard <jp@jpsim.com>

library/objective-c/EnvoyHTTPStreamImpl.m

@@ -75,7 +75,13 @@
   return NULL;
 }
 
-static void *ios_on_cancel_impl(envoy_stream_intel stream_intel, void *context) {
+// TODO(goaway) fix this up to call ios_on_send_window_available
+static void *ios_on_send_window_available(envoy_stream_intel stream_intel, void *context) {
+  return NULL;
+}
+
+static void *ios_on_cancel(envoy_stream_intel stream_intel,
+                           envoy_final_stream_intel final_stream_intel, void *context) {
   // This call is atomically gated at the call-site and will only happen once. It may still fire
   // after a complete response or error callback, but no other callbacks for the stream will ever
   // fire AFTER the cancellation callback.
@@ -94,11 +100,6 @@
   return NULL;
 }
 
-static void *ios_on_cancel(envoy_stream_intel stream_intel,
-                           envoy_final_stream_intel final_stream_intel, void *context) {
-  return ios_on_cancel_impl(stream_intel, context);
-}
-
 static void *ios_on_error(envoy_error error, envoy_stream_intel stream_intel,
                           envoy_final_stream_intel final_stream_intel, void *context) {
   ios_context *c = (ios_context *)context;
@@ -149,10 +150,10 @@ - (instancetype)initWithHandle:(envoy_stream_t)handle
   atomic_store(context->closed, NO);
 
   // Create native callbacks
-  // TODO(goaway) fix this up to call ios_on_send_window_available
-  envoy_http_callbacks native_callbacks = {ios_on_headers,  ios_on_data,        ios_on_metadata,
-                                           ios_on_trailers, ios_on_error,       ios_on_complete,
-                                           ios_on_cancel,   ios_on_cancel_impl, context};
+  envoy_http_callbacks native_callbacks = {
+      ios_on_headers, ios_on_data,     ios_on_metadata, ios_on_trailers,
+      ios_on_error,   ios_on_complete, ios_on_cancel,   ios_on_send_window_available,
+      context};
   _nativeCallbacks = native_callbacks;
 
   // We need create the native-held strong ref on this stream before we call start_stream because