USB: Remove the SAW_IRQ hcd flag

The HCD_FLAG_SAW_IRQ flag was introduced in order to catch IRQ routing
errors: If an URB was unlinked and the host controller hadn't gotten
any IRQs, it seemed likely that the IRQs were directed to the wrong
vector.

This warning hasn't come up in many years, as far as I know; interrupt
routing now seems to be well under control.  Therefore there's no
reason to keep the flag around any more.  This patch (as1495) finally
removes it.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>