Simplify away main history default
Passed non-regression STC
LLR: 2.97 (-2.94,2.94) <-1.75,0.25>
Total: 130752 W: 33725 L: 33605 D: 63422
Ptnml(0-2): 421, 15472, 33460, 15612, 411
https://tests.stockfishchess.org/tests/view/697eb9e35f56030af97b5a9e
Passed non-regression LTC
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 53352 W: 13697 L: 13509 D: 26146
Ptnml(0-2): 36, 5804, 14811, 5986, 39
https://tests.stockfishchess.org/tests/view/6980e5846362aee5c8a55396
closes https://github.com/official-stockfish/Stockfish/pull/6590
Bench: 2375860