staging: r8188eu: Remove no more necessary definitions and code

Remove no more necessary further 5GHz related code, along with no
more used definitions of macro and variables.

Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Link: https://lore.kernel.org/r/20210812002519.23678-4-fmdefrancesco@gmail.com


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