staging: rtl8188eu: remove MSG_88E macro from include/rtw_debug.h

Remove definition of MSG_88E macro from include/rtw_debug.h, as it
no longer has any callers and does not follow kernel coding conventions.
Removing this macro leaves only RT_TRACE and associated definitions.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210623234902.7411-10-phil@philpotter.co.uk


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