staging: rtl8188eu: remove core/rtw_debug.c

staging: rtl8188eu: remove core/rtw_debug.c

Remove core/rtw_debug.c as all the functions contained within it are
entirely unused, and modify the Makefile to remove it as a build
requirement. Also remove the function declarations from
include/rtw_debug.h - this is part of an ongoing effort to purge
dead/unused code and cleanup this driver. This has the helpful
side effect of removing all DBG_88E macro calls within this file
as well.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210615001507.1171-28-phil@philpotter.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>