Simplify lowply-history logic
Don't restrict usage to ttPv nodes exclusively
STC:
http://tests.stockfishchess.org/tests/view/5e5634f284a82b4acd41499a
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 152796 W: 29146 L: 29178 D: 94472
Ptnml(0-2): 2590, 17792, 35628, 17836, 2552
LTC:
http://tests.stockfishchess.org/tests/view/5e575d4984a82b4acd4149e8
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 20078 W: 2688 L: 2587 D: 14803
Ptnml(0-2): 139, 1914, 5853, 1973, 160
closes https://github.com/official-stockfish/Stockfish/pull/2565
bench: 4923286