hurd: Fix _hurd_select for single fd sets

hurd: Fix _hurd_select for single fd sets

The function attempts to optimize this case by performing one IPC system
call with the timeout included among the parameters, but in the absence
of a reply, it will call mach_msg again with the same timeout later,
effectively doubling the total timeout of the select/poll call.

Remove this optimization for the time being.

	* hurd/hurdselect.c (_hurd_select): Always call __io_select with no
	timeout.