Allow shallow depth pruning for horde pawn pushes

Allow shallow depth pruning for horde pawn pushes

horde STC
LLR: 2.95 (-2.94,2.94) [0.00,10.00]
Total: 1701 W: 905 L: 779 D: 17
http://35.161.250.236:6543/tests/view/5cb4d5d96e23db76ed252721

horde LTC
LLR: 2.97 (-2.94,2.94) [0.00,10.00]
Total: 1307 W: 708 L: 587 D: 12
http://35.161.250.236:6543/tests/view/5cb609536e23db76ed252731

giveaway STC
LLR: 2.96 (-2.94,2.94) [-10.00,5.00]
Total: 3966 W: 1558 L: 1529 D: 879
http://35.161.250.236:6543/tests/view/5cb4d6fd6e23db76ed25272a

kinglet STC
LLR: 2.99 (-2.94,2.94) [-10.00,5.00]
Total: 8117 W: 3649 L: 3644 D: 824
http://35.161.250.236:6543/tests/view/5cb4d7146e23db76ed25272c