staging: rtl8192u: remove GPL boiler plate text

The SPDX identifier is a legally binding shorthand, which
can be used instead of the full boiler plate text.

The file ieee80211_module.c has a proper SPDX line, so the
GPL boiler plate text is not needed.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20200703122604.12096-1-straube.linux@gmail.com


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