Revert futility pruning patches
reverts 09b6d28391cf582d99897360b225bcbbe38dd1c6 and
dbd7f602d3c7622df294f87d7239b5aaf31f695f that significantly impact mate
finding capabilities. For example on ChestUCI_23102018.epd, at 1M nodes,
the number of mates found is nearly reduced 2x without these depth conditions:
sf6 2091
sf7 2093
sf8 2107
sf9 2062
sf10 2208
sf11 2552
sf12 2563
sf13 2509
sf14 2427
master 1246
patched 2467
(script for testing at https://github.com/official-stockfish/Stockfish/files/6936412/matecheck.zip)
closes https://github.com/official-stockfish/Stockfish/pull/3641
fixes https://github.com/official-stockfish/Stockfish/issues/3627
Bench: 5467570