staging:rtl8192u: Remove unused UP2AC - Style

The macro UP2AC is commented out of the header file so the macro and its
associated comment are removed.

This is a coding style change which should have no impact on runtime
code execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>