staging: r8188eu: remove DBG_88E_LEVEL macro from include/rtw_debug.h

Remove the DBG_88E_LEVEL macro definition from include/rtw_debug.h, as
it has no callers and is surplus to requirements. This is motivated by
ongoing efforts to remove all non-standard debugging code from the
driver.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20211129002041.865-8-phil@philpotter.co.uk


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