NLL: re-triage all NLL-deferred issues (and delete NLL-deferred label)

The NLL team marked issues as NLL-deferred every time we wanted to leave something for "after the 2018 edition is out"

The edition is out. We want to re-triage those issues, probably now assigning them the P-high/P-medium/P-low priorities, and potentially also tagging them with NLL-{sound, complete, diagnostics} when appropriate.