sshpeer: make sshpeer.close() close the underlying connection

So the connection can be closed eagerly in future commits, instead of
relying on __del__.

Differential Revision: https://phab.mercurial-scm.org/D9995

mercurial/sshpeer.py

@@ -434,7 +434,7 b' class sshv1peer(wireprotov1peer.wirepeer'
         return True
 
     def close(self):
-        pass
+        self._cleanup()
 
     # End of ipeerconnection interface.