Python: remove settings object from objects pool

Change-Id: I4f21688f887c1ad99facb3ffe3a85b5918dd7daf
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/python/pythonsettings.cpp

@@ -708,6 +708,12 @@ PythonSettings::PythonSettings()
     pylspOptionsPage();
 }
 
+PythonSettings::~PythonSettings()
+{
+    ExtensionSystem::PluginManager::removeObject(this);
+    settingsInstance = nullptr;
+}
+
 void PythonSettings::init()
 {
     QTC_ASSERT(!settingsInstance, return );

src/plugins/python/pythonsettings.h

@@ -14,6 +14,8 @@ class PythonSettings : public QObject
     Q_OBJECT
 
 public:
+    ~PythonSettings();
+
     static void init();
 
     using Interpreter = ProjectExplorer::Interpreter;