[libFuzzer] Enable entropic by default.

Entropic has performed at least on par with vanilla scheduling on
Clusterfuzz, and has shown a slight coverage improvement on FuzzBench:
https://www.fuzzbench.com/reports/2020-08-31/index.html

Reviewed By: Dor1s

Differential Revision: https://reviews.llvm.org/D87476

GitOrigin-RevId: f3c2e0bcee64b0905addaefe9cd0c9ad4d20ac6f
3 files changed