[Import-sig] SIG charters

[Barry A. Warsaw]

Many of the sig deadlines have expired.  See www.python.org/sigs

Of these, the following appear to have no (or not much) meaningful
recent activity:

    do-sig
    import-sig
    types-sig

I propose to retire these sigs and extend all others for another year.

Objections?  <ducking>
-Barry