connection leak fix for aio-libs#253

Author: nbraem

aiohttp/connector.py

@@ -199,7 +199,6 @@ def _release(self, key, req, transport, protocol, *, should_close=False):
 
         reader = protocol.reader
         if should_close or (reader.output and not reader.output.at_eof()):
-            self._conns.pop(key, None)
             transport.close()
         else:
             conns = self._conns.get(key)