staging: wilc1000: remove unused functions

This patch removes unused function pointer hif_sync and hif_clear_int, and
removes it's related functions sdio_clear_int, sdio_sync, wilc_spi_clear_int
and wilc_spi_sync.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>