staging: rtl8188eu: remove DBG_88E macro definition

As all callers have now been removed, remove the definition of the
DBG_88E macro itself. It is no longer required and is dead code.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210615001507.1171-29-phil@philpotter.co.uk


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