wlan: remove obsolete ANI_CHIPSET_VOLANS featurization
The current code has ANI_CHIPSET_VOLANS conditional compilation.  This
conditional compilation was primarily used to flag functionality that
was new for Volans.  Since we are no longer supporting Volans with the
driver, remove the conditional compilation.  The associated code is
either removed or retained depending on whether or not it is
applicable to current chipsets.