Fix issue1789: The tutorial contained a misuse of the struct module.

(also remove an unneeded import struct from test_largefile)
diff --git a/Lib/test/test_largefile.py b/Lib/test/test_largefile.py
index 4dca97f..5731892 100644
--- a/Lib/test/test_largefile.py
+++ b/Lib/test/test_largefile.py
@@ -6,7 +6,7 @@
 #----------------------------------------------------------------------
 
 from test import test_support
-import os, struct, stat, sys
+import os, stat, sys
 
 try:
     import signal