Remove markdown.py and replace scattered uses of it.

It was used directly in two places in pages.py, I've
replaced those uses with safemarkdown calls. In the case
of the search fail page, I just removed the javascript
try-again link since it wouldn't be doable through safemarkdown
and that page isn't hit very frequently any more anyway.

r2/example.ini

@@ -312,7 +312,7 @@ takedown_sr = _takedowns
 png_optimizer = /usr/bin/env optipng
 # bad words that should be *'d out
 profanity_wordlist = 
-# which markdown backend to use (c = discount, py = markdown.py, snudown = snudown)
+# which markdown backend to use (c = discount, snudown = snudown)
 markdown_backend = snudown
 
 # -- search --