Android: simplify AndroidSdkManagerWidget::installEssentials()

Remove an argument that doesn't need to be be provided explicitly
by the caller and can be done internally.

Change-Id: Ie225f847560b746ce9b8103ab38caca5caca1b0a
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/android/androidsdkmanagerwidget.h

@@ -80,7 +80,7 @@ public:
                             QWidget *parent = nullptr);
     ~AndroidSdkManagerWidget() override;
 
-    void installEssentials(const QString &extraMessage = {});
+    void installEssentials();
 
 signals:
     void updatingSdk();