pass-through: fix unbinding of MSI interrupts

pass-through: fix unbinding of MSI interrupts

Commit 568da4f8 ("pt-irq fixes and improvements") went a little too far
in its cleaning up of pt_irq_destroy_bind(): While neither of the two
lists need any maintenance, the actual unbinding still needs to be
done. Fix this and at once
- move all variables applying only to the PCI/MSI-translate cases into
  scopes where they can't be used in error,
- limit the final (optional) log message to the cases it actually
  applies and enhance it to make clear how much cleaning up was
  actually done.

Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Sander Eikelenboom <linux@eikelenboom.it>