Remove their pieces from influencing 'unsafeSquares' in passer
evaluation.
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 36421 W: 8170 L: 8078 D: 20173
http://tests.stockfishchess.org/tests/view/
5d22fc8e0ebc5925cf0cb26e
LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 18927 W: 3253 L: 3129 D: 12545
http://tests.stockfishchess.org/tests/view/
5d26e2b20ebc5925cf0d3218
Closes https://github.com/official-stockfish/Stockfish/pull/2248
Bench:
3285659