Deprecating, and scheduling removal of, pg_dump's tar format.

Hi,

Is there any real reason to retain it? I realize it's not been a huge
issue to maintain the format, but it has significantly fewer features
than the other formats, without corresponding upsides (sql is clearer to
read, directory format has parallelism, custom is a single file while
allowing to select sub-sets of the data).  There's also the fact that it
creates temp files, which other formats don't.

Given the apparent lack of upside, it doesn't seem good to offer a
sub-par choice to our users.

If we were to remove it, it'd obviously be a drawn out affair, given
that we likely couldn't drop it from the restore side immediately...

Greetings,

Andres Freund