staging: rtl8192u: remove copying file

All source and header files have a GPL-2.0 SPDX identifier.
The 'copying' file with the whole GPL text is not needed, delete it.
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20200703122604.12096-2-straube.linux@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>