staging: rtl8712: Remove some unused #define and enum

These #define and the enum WIFI_REG_DOMAIN are unused.
They can be removed.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/6d5b505e7de20fdaba1831557baee1daf4656845.1625470822.git.christophe.jaillet@wanadoo.fr


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