refactor: Remove outdated comments, clean up code (gluonhq#613)

Author: AlmasB

app/src/main/java/com/oracle/javafx/scenebuilder/app/SceneBuilderApp.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2022, Gluon and/or its affiliates.
+ * Copyright (c) 2016, 2023, Gluon and/or its affiliates.
  * Copyright (c) 2012, 2014, Oracle and/or its affiliates.
  * All rights reserved. Use is subject to license terms.
  *
@@ -373,8 +373,7 @@ public void handleLaunch(List<String> files) {
         setApplicationUncaughtExceptionHandler();
 
         startInBackground("Set up Scene Builder", () -> {
-            backgroundStartPhase0();
-            backgroundStartPhase1();
+            backgroundStart();
             setUpUserLibrary(showWelcomeDialog);
             createEmptyDocumentWindow();
         });
@@ -843,34 +842,13 @@ private void performUseToolTheme(ToolTheme toolTheme) {
     private String getToolStylesheet() {
         return ResourceUtils.getToolStylesheet(toolTheme);
     }
-    
-    /*
-     * Background startup
-     * 
-     * To speed SB startup, we create two threads which anticipate some
-     * initialization tasks and offload the JFX thread:
-     *  - 'Phase 0' thread executes tasks that do not require JFX initialization
-     *  - 'Phase 1' thread executes tasks that requires JFX initialization
-     * 
-     * Tasks executed here must be carefully chosen:
-     * 1) they must be thread-safe
-     * 2) they should be order-safe : whether they are executed in background
-     *    or by the JFX thread should make no difference.
-     * 
-     * Currently we simply anticipate creation of big singleton instances
-     * (like Metadata, Preferences...)
-     */
-
-    private void backgroundStartPhase0() {
-        assert Platform.isFxApplicationThread() == false; // Warning 
 
+    /**
+     * This runs in a background thread to speed up SB startup.
+     */
+    private void backgroundStart() {
         PreferencesController.getSingleton();
         Metadata.getMetadata();
-    }
-
-    private void backgroundStartPhase1() {
-        assert Platform.isFxApplicationThread() == false; // Warning
-
         BuiltinLibrary.getLibrary();
         if (EditorPlatform.IS_MAC) {
             MenuBarController.getSystemMenuBarController();