Do not translate labels of boards submenus

Otherwise it may happen some weird sorting when untraslated and
translated labels are sorted together:

    Arduino megaAVR Boards
    Arduino nRF52 Board
    ESP32 Arduino
    ESP8266 Modules
    Schede Arduino AVR   <-- the localized string falls to the bottom

Also there is no way for 3rd party boards developers to actually provide
a translation, so let's just remove them.

app/src/processing/app/Base.java

@@ -1493,7 +1493,7 @@ public void actionPerformed(ActionEvent actionevent) {
         if (platformLabel == null)
           platformLabel = targetPackage.getId() + "-" + targetPlatform.getId();
 
-        JMenu platformBoardsMenu = new JMenu(tr(platformLabel));
+        JMenu platformBoardsMenu = new JMenu(platformLabel);
         MenuScroller.setScrollerFor(platformBoardsMenu);
         platformMenus.add(platformBoardsMenu);
 

arduino-core/src/processing/app/I18n.java

@@ -106,10 +106,6 @@ public static String format(String fmt, Object... args) {
    * This method is an hack to extract words with gettext tool.
    */
   protected static void unusedStrings() {
-    // These phrases are defined in the "platform.txt".
-    tr("Arduino AVR Boards");
-    tr("Arduino ARM (32-bits) Boards");
-
     // This word is defined in the "boards.txt".
     tr("Processor");
   }