Revert "Use the extra stack for 16bit USB and PS2 keyboard/mouse commands."

Revert "Use the extra stack for 16bit USB and PS2 keyboard/mouse commands."

It's not valid to pass a pointer to a stack variable through the
stack_hop() call (because the call changes the stack segment).  This
bug was probably not noticed before because by default
(CONFIG_ENTRY_EXTRASTACK) SeaBIOS uses the extra stack on all 16bit
entry points, and the internal stack_hop() with that config option is
effectively a no-op.

This reverts commit d488a7683d90bf8fae7ceb8c3ad9e95fbbd92079.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>