Remove duplicate line in Lib/http/client.py (#1665)

Author: remitamine

Lib/http/client.py

@@ -371,7 +371,6 @@ def _check_close(self):
         if self.version == 11:
             # An HTTP/1.1 proxy is assumed to stay open unless
             # explicitly closed.
-            conn = self.headers.get("connection")
             if conn and "close" in conn.lower():
                 return True
             return False