wireprotoserver: remove broken optimization for non-httplib client

There was an experimental non-httplib client in core for several
years. It was removed a week or so ago.

We kept the optimization for this client in the server code. I'm
not sure if that was intended or not. But it doesn't matter: the
code was wrong.

Because the code was accessing a WSGI environment dict, it needed to
access the HTTP_X_HGHTTP2 key to actually read the HTTP header. So
the code deleted by this commit wasn't actually doing anything
meaningful. Doh.

Differential Revision: https://phab.mercurial-scm.org/D2741

mercurial/wireprotoserver.py

@@ -328,10 +328,7 b' def _handlehttperror(e, wsgireq, cmd):'
     if (wsgireq.env[r'REQUEST_METHOD'] == r'POST' and
         # But not if Expect: 100-continue is being used.
         (wsgireq.env.get('HTTP_EXPECT',
-                         '').lower() != '100-continue') or
-        # Or the non-httplib HTTP library is being advertised by
-        # the client.
-        wsgireq.env.get('X-HgHttp2', '')):
+                         '').lower() != '100-continue')):
         wsgireq.drain()
     else:
         wsgireq.headers.append((r'Connection', r'Close'))