staging: rtl8188eu: remove GlobalDebugLevel variable

Remove GlobalDebugLevel variable and all of its uses, as it is now
no longer used anywhere in this driver.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210625000756.6313-23-phil@philpotter.co.uk


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