Removed unnecessary header

The xkbcommon-keysyms.h header isn't available on some older systems,
and we don't actually need it for this code.

src/events/SDL_keysym_to_scancode.c

@@ -26,7 +26,6 @@
 #include "SDL_keyboard_c.h"
 #include "SDL_scancode_tables_c.h"
 
-#include <xkbcommon/xkbcommon-keysyms.h>
 #include <xkbcommon/xkbcommon.h>
 
 /* *INDENT-OFF* */ /* clang-format off */