use lambda function instead of private method

src/app/browser/main/tab/label.cpp

@@ -20,10 +20,13 @@ Label::Label(
         controller->signal_pressed().connect(
             [this](int n, double x, double y)
             {
-                on_click(
-                    n, x, y
+                if (n == 2) // double click
+                {
+                    activate_action(
+                        "win.tab_close"
                     );
                 }
+            }
         );
 
         add_controller(
@@ -32,16 +35,3 @@ Label::Label(
 }
 
 Label::~Label() = default;
-
-void Label::on_click(
-    int n,
-    double x,
-    double y
-) {
-    if (n == 2) // double click
-    {
-        activate_action(
-            "win.tab_close"
-        );
-    }
-}

src/app/browser/main/tab/label.hpp

@@ -13,12 +13,6 @@ namespace app::browser::main::tab
     {
         Glib::RefPtr<Gtk::GestureClick> controller;
 
-        void on_click(
-            int n,
-            double x,
-            double y
-        );
-
         public:
 
             Label(