Re: cutting down the TODO list thread

Here I'm just reviewing a couple items in the Sorting section:

- Consider whether duplicate keys should be sorted by block/offset

https://www.postgresql.org/message-id/flat/23321.1205726381%40sss.pgh.pa.us

It's moot since we started requiring tid as a tiebreaker for btree indexes, so I'll just remove this.

- Consider being smarter about memory and external files used during sorts

https://www.postgresql.org/message-id/1196186626.4246.1078.camel@ebony.site

We've had a large number of improvements in this area since 2007, and it seems the ideas in this thread have mostly been done or superseded already.