Python: Remove pluginInstance() and convert users

Change-Id: I43179961cdee855b710fc082568a7d0d9a0f0719
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/python/pythonsettings.h

@@ -59,6 +59,8 @@ public slots:
     void listDetectedPython(const QString &detectionSource, QString *logMessage);
 
 private:
+    void disableOutdatedPyls();
+    void disableOutdatedPylsNow();
     void fixupPythonKits();
     void initFromSettings(Utils::QtcSettings *settings);
     void writeToSettings(Utils::QtcSettings *settings);