LibGUI: Remove unused Widget backcolor/forecolor properties

These were some leftovers from the VisualBuilder times.

Applications/DisplaySettings/DisplaySettings.cpp

@@ -93,7 +93,6 @@ void DisplaySettingsWidget::create_frame()
 
     auto& settings_content = m_root_widget->add<GUI::Widget>();
     settings_content.set_layout<GUI::VerticalBoxLayout>();
-    settings_content.set_backcolor("red");
     settings_content.set_background_color(Color::Blue);
     settings_content.set_background_role(Gfx::ColorRole::Window);
     settings_content.layout()->set_margins({ 4, 4, 4, 4 });

Libraries/LibGUI/Widget.cpp

@@ -838,22 +838,6 @@ void Widget::focus_next_widget(FocusSource source)
     }
 }
 
-void Widget::set_backcolor(const StringView& color_string)
-{
-    auto color = Color::from_string(color_string);
-    if (!color.has_value())
-        return;
-    set_background_color(color.value());
-}
-
-void Widget::set_forecolor(const StringView& color_string)
-{
-    auto color = Color::from_string(color_string);
-    if (!color.has_value())
-        return;
-    set_foreground_color(color.value());
-}
-
 Vector<Widget*> Widget::child_widgets() const
 {
     Vector<Widget*> widgets;

Libraries/LibGUI/Widget.h

@@ -220,9 +220,6 @@ public:
     void set_background_color(Color color) { m_background_color = color; }
     void set_foreground_color(Color color) { m_foreground_color = color; }
 
-    void set_backcolor(const StringView&);
-    void set_forecolor(const StringView&);
-
     void set_autofill(bool b) { set_fill_with_background_color(b); }
 
     Window* window()