staging: rtl8192u: remove #ifndef RTL8192U and the code inside it

This patch removes the unused code inside #ifndef RTL8192U header guard
and the guard itself, since RTL8192U is defined.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>