With the recent changes to the order of processing key bindings
(`GlobalAction`s are handled first), having the alt-wheel bindings in here causes a
regression as they are handled before `OnScroll` events.
Specifically, this means editor alt-scroll functionality no longer works
with the default bindings.
Removing the bindings fixes this, while also still allowing alt-wheel
adjustment of the volume via `VolumeControlReceptor`:
a2f50af424/osu.Game/Overlays/Volume/VolumeControlReceptor.cs (L21-L26)
In conjunction with the special case in `OsuScrollContainer`:
02d5b1352b/osu.Game/Graphics/Containers/OsuScrollContainer.cs (L103-L105)
