This reverts commit fd2997c2db.
Core tests are no longer online, so no longer are flaky nor tie up many
minutes of test runner time. So re-enable for all jobs.
They're still slightly flaky even with insanely long timeouts, and even when not they waste a huge amount of our runner time sitting and waiting for the DHT to disconnect and reconnect.
Still run on our fedora job to get almost all of the benefit, plus AddressSanitizer is enabled there for better testing synergy.
