staging: rtl8192u: remove unused files

I was doing some code audits looking at scattergather uses, and noticed
that update() in drivers/staging/rtl8192u/ieee80211/digest.c uses
sg.page which doesn't exist any longer, so this can't possibly compile.

Turns out that digest.c is actually unused.  It doesn't get referenced
in a Makefile or get compiled and doesn't get used as far as I can see.
I then widened the search to all the files in the directory.  There are
a *bunch* that look unused.  I removed all of them, then added them
back one at a time until the driver compiled again.

Signed-off-by: Dave Hansen <dave.hansen@intel.com>
Cc: jerry-chuang@realtek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>