staging: r8188eu: remove HW_VAR_ACK_PREAMBLE from SetHwReg8188EU()

Remove the HW_VAR_ACK_PREAMBLE case from SetHwReg8188EU() and move
its functionality to rtw_wlan_util.c where it is actually used. This
is part of the ongoing effort to get rid of the unwanted hal layer.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220402092332.6627-3-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>