xdg-shell: Remove the serial from popup_done

It doesn't serve any purpose, as it's a serial that the client gave to
the server when starting the popup, which the client already has.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/clients/window.c b/clients/window.c
index 7b12227..d919210 100644
--- a/clients/window.c
+++ b/clients/window.c
@@ -4727,7 +4727,7 @@
 }
 
 static void
-handle_popup_popup_done(void *data, struct xdg_popup *xdg_popup, uint32_t serial)
+handle_popup_popup_done(void *data, struct xdg_popup *xdg_popup)
 {
 	struct window *window = data;
 	struct menu *menu = window->main_surface->widget->user_data;
diff --git a/desktop-shell/shell.c b/desktop-shell/shell.c
index 076b454..b081e33 100644
--- a/desktop-shell/shell.c
+++ b/desktop-shell/shell.c
@@ -3315,8 +3315,7 @@
 	if (shell_surface_is_wl_shell_surface(shsurf))
 		wl_shell_surface_send_popup_done(shsurf->resource);
 	else if (shell_surface_is_xdg_popup(shsurf))
-		xdg_popup_send_popup_done(shsurf->resource,
-					  shsurf->popup.serial);
+		xdg_popup_send_popup_done(shsurf->resource);
 }
 
 static void
diff --git a/protocol/xdg-shell.xml b/protocol/xdg-shell.xml
index 6abfabd..d0a2124 100644
--- a/protocol/xdg-shell.xml
+++ b/protocol/xdg-shell.xml
@@ -415,7 +415,6 @@
 	that is, when the users clicks a surface that doesn't belong
 	to the client owning the popup surface.
       </description>
-      <arg name="serial" type="uint" summary="serial of the implicit grab on the pointer"/>
     </event>
 
   </interface>