Staging: wlan-ng: Remove unused functions and prototypes

hfa384x_drvr_getconfig_async is not used anywhere in the kernel
so remove it. Also remove its prototype from the header file. Also
the function hfa384x_cb_rrid was only used by hfa384x_drvr_getconfig_async
so remove its definition and prototype as well.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>