hgweb: replace PATH_INFO with dispatchpath

This was the last consumer of wsgireq.env from our WSGI applications!

(Although indirect consumers of this attribute exist in
wsgirequest.respond().)

Differential Revision: https://phab.mercurial-scm.org/D2825

mercurial/hgweb/hgwebdir_mod.py

@@ -369,7 +369,7 b' class hgwebdir(object):'
                 res.headers['Content-Security-Policy'] = csp
                 wsgireq.headers.append(('Content-Security-Policy', csp))
 
-            virtual = wsgireq.env.get("PATH_INFO", "").strip('/')
+            virtual = req.dispatchpath.strip('/')
             tmpl = self.templater(wsgireq, nonce)
             ctype = tmpl('mimetype', encoding=encoding.encoding)
             ctype = templater.stringify(ctype)