Ignore mouse motion events

[ceski-1]

We only use SDL_GetMouseState() and SDL_GetRelativeMouseState(). so SDL_MOUSEMOTION events were already being ignored. This also prevents them from getting added to queue, so they aren't processed by SDL_PollEvent().

• https://github.com/libsdl-org/SDL/blob/SDL2/src/events/SDL_mouse.c#L599-L606
• https://github.com/libsdl-org/SDL/blob/SDL2/src/events/SDL_mouse.c#L650-L674
• https://github.com/libsdl-org/SDL/blob/SDL2/src/events/SDL_mouse.c#L997-L1023