staging: wfx: remove remaining code of 'secure link' feature

Commit e8d607ce ("staging: wfx: drop 'secure link' feature") had
removed the 'secure link' feature. However, a few lines of codes were
yet here.

Fixes: e8d607ce

 ("staging: wfx: drop 'secure link' feature")
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20201007101943.749898-3-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>