Drop Timer/Tween user_data Can use lambdas/bind for this, also hasn't made it into a release so shouldn't break anything

diff --git a/32blit/engine/timer.hpp b/32blit/engine/timer.hpp
index 3a8f166..a96f9cf 100644
--- a/32blit/engine/timer.hpp
+++ b/32blit/engine/timer.hpp

@@ -9,7 +9,6 @@
     using TimerCallback = std::function<void (Timer &timer)>;
 
     TimerCallback callback = nullptr;
-    void *user_data = nullptr;
 
     uint32_t duration = 0;                  // how many milliseconds between callbacks
     uint32_t started = 0;                   // system time when timer started in milliseconds

diff --git a/32blit/engine/tweening.hpp b/32blit/engine/tweening.hpp
index 203cb32..a181ee4 100644
--- a/32blit/engine/tweening.hpp
+++ b/32blit/engine/tweening.hpp

@@ -9,7 +9,6 @@
   struct Tween {
     using TweenFunction = std::function<float(uint32_t t, float b, float c, uint32_t d)>;
     TweenFunction function = nullptr;
-    void *user_data = nullptr;
 
     float from = 0.0f;
     float to = 1.0f;