Expects: AX    001fH
Returns: AX    status: 001fH=deactivated OK
ffffH=can't deactivate
ES:DX address of previous INT 33H handler
Info: This deactivates the mouse driver.  All interrupts used by the
mouse support are disabled, effectively eliminating all mouse

Use INT 33H 0021H to re-enable all interrupts used by the mouse

Note that the INT 33H vector remains in place, but the only
function it can perform is INT 33H 0021H (to re-enable).

You might call this just before replacing the mouse support with
your own system of interrupts and kludges.  Then use the return
value in ES:DX to reinstall the previous INT 33H code at some
later time (i.e., when you exit to DOS).

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INT 33H 001fH: Deactivate Mouse Driver