[NO MERGE] optimize fee estimation test, re-include in regular list

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Turning off mempool consistency checks sped up this test by 30%.

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Actually seems to work reasonably. Test took under 500 seconds, and whole suite in about 44 minutes.

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It's passing consistently. Restarting one more time, @stevenroose could you ACK/merge if it passes again?

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interesting, the section where it's supposed to recover in a few seconds failed to.

Timed out at this section:

# Don't make a block, race condition when pegin-invalid block
        # is awaiting further validation, nodes reject subsequent blocks
        # even ones they create
        print("Now waiting for node to re-evaluate peg-in witness failed block... should take a few seconds")
        self.sync_all(self.node_groups)
        print("Completed!\n")

One mempool was missing a tx to the end of the test. Wonder what happened there... leaving this PR open then.