web: prevent TypeError thrown when using the diffstat templates

Remove the lambda used to wrap webutil.diffstat because:
- functions passed to the templater must accept keyword arguments
- webutil.diffstat is a generator, so already calculates the diffstat lazily

This reverts the changes made to 1d3e2349304a after it was submitted to the
mailing list but before it was queued.

mercurial/hgweb/webcommands.py

@@ -271,7 +271,7 b' def changeset(web, req, tmpl):'
     diffs = webutil.diffs(web.repo, tmpl, ctx, None, parity, style)
 
     parity = paritygen(web.stripecount)
-    diffstat = lambda: webutil.diffstat(tmpl, ctx, parity)
+    diffstat = webutil.diffstat(tmpl, ctx, parity)
 
     return tmpl('changeset',
                 diff=diffs,