Core: Remove SettingsDatabase QObject base

Was not really needed except for the ownership.

Change-Id: I88e32123cbb85a8217ade9450b5b578845736311
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/coreplugin/mainwindow.cpp

@@ -124,8 +124,7 @@ MainWindow::MainWindow()
     , m_lowPrioAdditionalContexts(Constants::C_GLOBAL)
     , m_settingsDatabase(
           new SettingsDatabase(QFileInfo(PluginManager::settings()->fileName()).path(),
-                               QCoreApplication::applicationName(),
-                               this))
+                               QCoreApplication::applicationName()))
     , m_progressManager(new ProgressManagerPrivate)
     , m_jsExpander(JsExpander::createGlobalJsExpander())
     , m_vcsManager(new VcsManager)
@@ -307,6 +306,9 @@ MainWindow::~MainWindow()
 
     delete m_jsExpander;
     m_jsExpander = nullptr;
+
+    delete m_settingsDatabase;
+    m_settingsDatabase = nullptr;
 }
 
 void MainWindow::init()