Handle mouse integer scrolling locally

Do not rely on SDL to expose integer scroll values, as they are not
available in all versions.

It was reimplemented in SDL 3.2.12 by this commit:
<0447c2f3c3>

Refs #6156 <https://github.com/Genymobile/scrcpy/issues/6156>

app/src/input_manager.c

@@ -903,8 +903,6 @@ sc_input_manager_process_mouse_wheel(struct sc_input_manager *im,
         .hscroll = event->x,
         .vscroll = event->y,
 #endif
-        .hscroll_int = event->x,
-        .vscroll_int = event->y,
         .buttons_state = im->mouse_buttons_state,
     };