staging: wilc1000: clean up sleep wrapper

The driver has a simple wrapper around msleep, as well as
a more advanced sleep function that is unused. This removes
the unused code and the options to turn the feature on or
off.

A follow-up should rework the code to use msleep directly.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>