removed unused function in SettingsDialog

src/widgets/dialogs/SettingsDialog.cpp

@@ -20,8 +20,6 @@
 
 namespace chatterino {
 
-SettingsDialog *SettingsDialog::instance_ = nullptr;
-
 SettingsDialog::SettingsDialog()
     : BaseWindow(BaseWindow::DisableCustomScaling)
 {
@@ -138,11 +136,6 @@ void SettingsDialog::filterElements(const QString &text)
     }
 }
 
-SettingsDialog *SettingsDialog::instance()
-{
-    return SettingsDialog::instance_;
-}
-
 void SettingsDialog::addTabs()
 {
     this->ui_.tabContainer->setMargin(0);