rtl8723au: Remove dead code assocoated with CONFIG_HW_ANTENNA_DIVERSITY

AFAIK, this parameter is only valid for 92C, 92D, and 88E chips. In any
case, it is not selected here.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
rtl8723au: Remove CONFIG_ANTENNA_DIVERSITY

This parameter is not selected.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
rtl8723au: Remove dead code associated with CONFIG_SW_ANTENNA_DIVERSITY

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>