gtkui: Remove hack that made the left mouse button behave like the mi…

…ddle button as it breaks the intended behavior of GtkSlider in GTK+ 3.5.x. Closes: #138.

src/gtkui/ui_gtk.c

@@ -309,23 +309,12 @@ static gboolean ui_slider_change_value_cb(GtkRange * range, GtkScrollType scroll
 static gboolean ui_slider_button_press_cb(GtkWidget * widget, GdkEventButton * event, gpointer user_data)
 {
     slider_is_moving = TRUE;
-
-    /* HACK: clicking with the left mouse button moves the slider
-       to the location of the click. */
-    if (event->button == 1)
-        event->button = 2;
-
     return FALSE;
 }
 
 static gboolean ui_slider_button_release_cb(GtkWidget * widget, GdkEventButton * event, gpointer user_data)
 {
-    /* HACK: see ui_slider_button_press_cb */
-    if (event->button == 1)
-        event->button = 2;
-
     slider_is_moving = FALSE;
-
     return FALSE;
 }