Cygwin: don't copy path_conv in fhandler_base::reset

Cygwin: don't copy path_conv in fhandler_base::reset

There's a slim chance that duplicating fhandlers may end up duplicating
path_conv_handle handles twice ending up with a handle leak, due to
fhandler_base::reset calling path_conv::operator<< after the only
caller, fhandler::copyto, already called path_conv::operator=.

Just drop the call which basically duplicates what path_conv::operator=
already did.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>