Staging: panel: remove support for smartcards

Smartcard support was more like a proof-of-concept than a completed
work. It was only able to read serial numbers from a few smartcards,
and the goal was to be able to secure keypad access with a smartcard.
Given how the concept was limited, this was never used beyond demos,
and it's better to remove this code so that nobody tries to use it
for security purposes.

The function panel_bind_callback() was ifdef'ed out, as its only user
was smartcard. However, it would be a waste to remove it because many
variations made on this driver will need it.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Cc: Frank Menne <frank.menne@hsm.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>