snapdiff: Drop the --version option

This isn't currently giving any actual information, and it doesn't fit
well with the new top-level apitrace command, (which should presumably
take care of any --version option itself).
diff --git a/scripts/snapdiff.py b/scripts/snapdiff.py
index 0ed3937..13e5069 100755
--- a/scripts/snapdiff.py
+++ b/scripts/snapdiff.py
@@ -138,8 +138,7 @@
     global options
 
     optparser = optparse.OptionParser(
-        usage="\n\t%prog [options] <ref_prefix> <src_prefix>",
-        version="%%prog")
+        usage="\n\t%prog [options] <ref_prefix> <src_prefix>")
     optparser.add_option(
         '-o', '--output', metavar='FILE',
         type="string", dest="output", default='index.html',