GUI2/End Credits: use DRAW event hook to scroll text instead of a timer

There's no visual difference between these methods since any of the scroll position changes wouldn't
take effect until the next draw anyway

src/gui/dialogs/end_credits.cpp

@@ -19,7 +19,6 @@
 #include "config.hpp"
 #include "game_config.hpp"
 #include "gui/auxiliary/find_widget.hpp"
-#include "gui/core/timer.hpp"
 #include "gui/widgets/grid.hpp"
 #include "gui/widgets/repeating_button.hpp"
 #include "gui/widgets/scrollbar.hpp"
@@ -42,20 +41,11 @@ REGISTER_DIALOG(end_credits)
 end_credits::end_credits(const std::string& campaign)
 	: focus_on_(campaign)
 	, backgrounds_()
-	, timer_id_()
 	, text_widget_(nullptr)
 	, scroll_speed_(100)
 {
 }
 
-end_credits::~end_credits()
-{
-	if(timer_id_ != 0) {
-		remove_timer(timer_id_);
-		timer_id_ = 0;
-	}
-}
-
 static void parse_about_tag(const config& cfg, std::stringstream& ss)
 {
 	if(!cfg.has_child("entry")) {
@@ -73,11 +63,12 @@ void end_credits::pre_show(window& window)
 {
 	window.set_callback_next_draw([this]()
 	{
-		timer_id_ = add_timer(10, std::bind(&end_credits::timer_callback, this), true);
 		// Delay a little before beginning the scrolling
 		last_scroll_ = SDL_GetTicks() + 3000;
 	});
 
+	window.connect_signal<event::DRAW>(std::bind(&end_credits::timer_callback, this), event::dispatcher::front_child);
+
 	connect_signal_pre_key_press(window, std::bind(&end_credits::key_press_callback, this, _5));
 
 	std::stringstream ss;
@@ -160,10 +151,6 @@ void end_credits::timer_callback()
 	text_widget_->set_vertical_scrollbar_item_position(cur_pos + needed_dist);
 
 	last_scroll_ = now;
-
-	if(text_widget_->vertical_scrollbar_at_end()) {
-		remove_timer(timer_id_);
-	}
 }
 
 void end_credits::key_press_callback(const SDL_Keycode key)

src/gui/dialogs/end_credits.hpp

@@ -34,8 +34,6 @@ class end_credits : public modal_dialog
 public:
 	explicit end_credits(const std::string& campaign);
 
-	~end_credits();
-
 	static void display(CVideo& video, const std::string& campaign = "")
 	{
 		end_credits(campaign).show(video);
@@ -55,8 +53,6 @@ class end_credits : public modal_dialog
 
 	std::vector<std::string> backgrounds_;
 
-	size_t timer_id_;
-
 	scroll_label* text_widget_;
 
 	// The speed of auto-scrolling, specified as px/s