More copyright header updates

Remove old copyrights from files added recently (for 4.6 or somewhat
earlier, plus some selected files where it was easier to enumerate all
years than to adapt the script to handle their existing copyrights) and
make the copyright headers follow the new format.  Put best-guess
estimates for the copyright years based on when the files have been
modified.  No effort was spent on trying to track content beyond git
rename detection, so some content may originate from earlier than the
first copyright year mentioned, but this is hopefully not a big deal.

Part of #818.

Change-Id: I44e1eff552bff47a2ae10b3181960a8a2a6753df