[fuchsia] Fix up includes of Zircon headers (#4842)

content_handler/rasterizer.h

@@ -7,10 +7,11 @@
 
 #include <memory>
 
+#include <zx/eventpair.h>
+
 #include "flutter/flow/layers/layer_tree.h"
 #include "lib/fxl/functional/closure.h"
 #include "lib/fxl/macros.h"
-#include "zircon/system/ulib/zx/include/zx/eventpair.h"
 
 namespace flutter_runner {
 

content_handler/session_connection.h

@@ -5,6 +5,8 @@
 #ifndef FLUTTER_CONTENT_HANDLER_SESSION_CONNECTION_H_
 #define FLUTTER_CONTENT_HANDLER_SESSION_CONNECTION_H_
 
+#include <zx/eventpair.h>
+
 #include "flutter/common/threads.h"
 #include "flutter/content_handler/vulkan_surface_producer.h"
 #include "flutter/flow/compositor_context.h"
@@ -14,7 +16,6 @@
 #include "lib/fxl/macros.h"
 #include "lib/ui/scenic/client/resources.h"
 #include "lib/ui/scenic/client/session.h"
-#include "zircon/system/ulib/zx/include/zx/eventpair.h"
 
 namespace flutter_runner {