This fixes various minor problems:

- re-orders some tests so that "(no bus?)" diagnostic should
    no longer be appearing (and making folk worry needlessly)

- removes one unreachable test for URB_TIMEOUT_KILLED

- removes the reachable test, since it's never an error on the
    part of the device driver to unlink something the HCD is already
    unlinking.

- gets rid of some comments and code that expected automagic resubmits
    for interrupts (no more!),

- resolves a FIXME for a rather unlikely situation (HCD can't
    perform the unlink, it reports an error)

It also starts to use dev_dbg() macros, which give more concise
(lately) and useful (they have both driver name and device id)
diagnostics than the previous usb-only dbg() macros.  To do this,
DEBUG had to be #defined before <linux/driver.h> is included, but
it can't be #undeffed before <linux/kernel.h> is included.