Remove reindex_catalog test from test schedules.

As the test currently causes occasional deadlocks (due to the schema
cleanup from previous sessions potentially still running), and the
patch from f912d7de has gotten a fair bit of buildfarm coverage,
remove the test from the test schedules. There's a set of minor
releases coming up.

Leave the tests in place, so it can manually be run using EXTRA_TESTS.

For now also leave it in master, as there's no imminent release, and
there's plenty (re-)index related work in 12. But we'll have to
disable it before long there too, unless somebody comes up with simple
enough fixes for the deadlock (I'm about to post a vague idea to the
list).

Discussion: https://postgr.es/m/4622.1556982247@sss.pgh.pa.us
Backpatch: 9.4-11 (no master!)