Revert "Test that vacuum removes tuples older than OldestXmin"

Revert "Test that vacuum removes tuples older than OldestXmin"

This reverts commit 80c34692e8e674e3b2f150f248ef2002ae2ac3a7.

This test proved to be unstable on the buildfarm, timing out before the
standby could catch up on 32-bit machines where more rows were required
and failing to reliably trigger multiple index vacuum rounds on 64-bit
machines where fewer rows should be required.

Because the instability is only known to be present on versions of
Postgres with TIDStore used for dead TID storage by vacuum, this is only
being reverted on master and REL_17_STABLE.

As having this coverage may be valuable, there is a discussion on the
thread of possible ways to stabilize the test. If that happens, a fixed
test can be committed again.

Backpatch-through: 17
Reported-by: Tom Lane
Discussion: https://postgr.es/m/614152.1721580711%40sss.pgh.pa.us