staging: wilc1000: change_virtual_intf: change codes for unified firmware

In previous patch, we use unified firmware on wilc, which means we do not need
to download firmware again to change virtual interfaces.
There are a lot of codes to change interface and they are needless now, so
remove them except wilc_set_operation_mode function which change the mode and
wilc_set_power_mgmt which control power save.
There will be unused functions and they will be removed in later patch.

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