strip out update/render/repaint window cruft; promote layer per-tick APIs to base layer

src/os/gfx/linux/os_gfx_linux.c

@@ -142,12 +142,6 @@ os_window_first_paint(OS_Handle handle)
   XMapWindow(os_lnx_gfx_state->display, w->window);
 }
 
-internal void
-os_window_equip_repaint(OS_Handle handle, OS_WindowRepaintFunctionType *repaint, void *user_data)
-{
-  if(os_handle_match(handle, os_handle_zero())) {return;}
-}
-
 internal void
 os_window_focus(OS_Handle handle)
 {