Changes to the deprecation-removal timeline

With RFC-945 now implemented, the minimum time between deprecation and removal is now one major release (not two) or eight weeks, whichever is larger (full policy here).

On DM-40057, I’ve taken the liberty of updating any deprecation messages that say “will be removed after v27” to say “will be removed after v26” instead, since those are the ones that haven’t yet appeared in a major release. I’ve used a GitHub search in the LSST org to spot those cases, so I think I’ve found them all, but I’ve added a links from DM-40057 to the removal tickets for each deprecation warning I adjusted (creating a few previously-missing removal tickets in the process), so you can check out that ticket’s links to see if I’ve included your favorite.

Please let me know ASAP if there are any I’ve missed, or if you’d prefer to keep the original removal timeline for any particular deprecations.