Remove unused present method

This is now done by the FlutterCompositor.present_layers_callback.

engine/src/flutter/shell/platform/linux/fl_engine.cc

@@ -203,13 +203,7 @@ static uint32_t fl_engine_gl_get_fbo(void* user_data) {
 }
 
 static bool fl_engine_gl_present(void* user_data) {
-  FlEngine* self = static_cast<FlEngine*>(user_data);
-  g_autoptr(GError) error = nullptr;
-  gboolean result = fl_renderer_present(self->renderer, &error);
-  if (!result) {
-    g_warning("%s", error->message);
-  }
-  return result;
+  return true;
 }
 
 static bool fl_engine_gl_make_resource_current(void* user_data) {

engine/src/flutter/shell/platform/linux/fl_renderer.cc

@@ -121,10 +121,6 @@ guint32 fl_renderer_get_fbo(FlRenderer* self) {
   return 0;
 }
 
-gboolean fl_renderer_present(FlRenderer* self, GError** error) {
-  return TRUE;
-}
-
 gboolean fl_renderer_create_backing_store(
     FlRenderer* self,
     const FlutterBackingStoreConfig* config,

engine/src/flutter/shell/platform/linux/fl_renderer.h

@@ -186,18 +186,6 @@ gboolean fl_renderer_clear_current(FlRenderer* renderer, GError** error);
  */
 guint32 fl_renderer_get_fbo(FlRenderer* renderer);
 
-/**
- * fl_renderer_present:
- * @renderer: an #FlRenderer.
- * @error: (allow-none): #GError location to store the error occurring, or %NULL
- * to ignore.
- *
- * Presents the current frame.
- *
- * Returns %TRUE if successful.
- */
-gboolean fl_renderer_present(FlRenderer* renderer, GError** error);
-
 /**
  * fl_renderer_create_backing_store:
  * @renderer: an #FlRenderer.