Simplify space evaluation for drop variants

Simplify space evaluation for drop variants

crazyhouse STC
LLR: 2.98 (-2.94,2.94) [-10.00,5.00]
Total: 3579 W: 1749 L: 1708 D: 122
http://www.variantfishtest.org:6543/tests/view/5fdf73c16e23db221d9e95f5

crazyhouse LTC
LLR: 2.95 (-2.94,2.94) [-10.00,5.00]
Total: 945 W: 484 L: 425 D: 36
http://www.variantfishtest.org:6543/tests/view/5fe1b6c56e23db221d9e9653

shogi STC
LLR: -2.98 (-2.94,2.94) [-10.00,5.00]
Total: 4773 W: 2324 L: 2427 D: 22
http://www.variantfishtest.org:6543/tests/view/5fdf73d36e23db221d9e95f8

shogi LTC
LLR: 2.97 (-2.94,2.94) [-10.00,5.00]
Total: 3545 W: 1785 L: 1742 D: 18
http://www.variantfishtest.org:6543/tests/view/5fe1b6b06e23db221d9e9651