How do I disconnect a garbage disposal wall switch?
It depends on  the wiring in the switch box. More than likely there are two (or more) sets of wires coming into the box and disconnecting and removing the switch still   means it is junction box. By code; a junction box Can not be covered or buried in the wall.  The box must have a cover that can be removed for access to the wires.
You would have to   remove both/all wires all the way back to their source, which would  mean opening walls because the wires are stapled to the studs (unless they are run in conduit) and they may originate some distance from the box.
The air switch Eliminates the need for the wall switch but the power to the outlet for the disposal is still needed, and it is probably coming from the box that houses the switch.