staging: r8188eu: remove 5 GHz code

The driver is for chips that do not operate in the 5 GHz band.
Remove some 5 GHz related code.

Acked-by: Phillip Potter <phil@philpotter.co.uk>
Acked-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210823193028.12391-1-straube.linux@gmail.com


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