staging: wilc1000: remove os_context

This patch removes variable os_context of wilc_sdio_t and wilc_spi_t because
os_context is not used, and delete it's related code.

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