libcacard is now a standalone project hosted with the Spice project (see
the 2.5.0 release announcement), remove it from qemu tree.

Use the library if found during configure or if --enable-smartcard.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Paolo Bonzini <pbonzini@redhat.com>