Revert "Performance tests: recover a baseline from ancestor commits and CI…

Authored by bgamari on Jan 31 2019, 6:47 PM.

Description

Revert "Performance tests: recover a baseline from ancestor commits and CI results."

Unfortunately this has broken all future commits due to spurious(?)
performance changes which I have been unable to work around.

This reverts commit cc2261d42f6a954d88e355aaad41f001f65c95da.