[scenic] Remove includes of lib/ui/scenic/fidl_helpers.h

This header should no longer be needed.

Test: Compiles.
Change-Id: I040bf475a058ebd3dcae1e7b6390b16a94586e5d
diff --git a/runtime/flutter_runner/session_connection.cc b/runtime/flutter_runner/session_connection.cc
index 16d4679..51ae1e2 100644
--- a/runtime/flutter_runner/session_connection.cc
+++ b/runtime/flutter_runner/session_connection.cc
@@ -6,7 +6,7 @@
 
 #include "flutter/fml/make_copyable.h"
 #include "lib/fidl/cpp/optional.h"
-#include "lib/ui/scenic/fidl_helpers.h"
+#include "lib/ui/scenic/cpp/commands.h"
 #include "vsync_recorder.h"
 #include "vsync_waiter.h"