staging: wilc1000: remove unnecessary extern function declaration

Function NetworkInfoReceived, GnrlAsyncInfoReceived and
host_int_ScanCompleteReceived are declared in the header file already.
Just removes the declaration and comments.

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