Simplify KingProtector penalty.
Recent tuning results implied this penalty is more important for knights
and bishops, and almost negligible for rooks and queen.
Passed as simplification both
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 20873 W: 4592 L: 4469 D: 11812
http://tests.stockfishchess.org/tests/view/5b2fb4d00ebc5902b2e57e84
and LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 46069 W: 7949 L: 7870 D: 30250
http://tests.stockfishchess.org/tests/view/5b2fcc4b0ebc5902b2e580c5
Closes https://github.com/official-stockfish/Stockfish/pull/1660
Bench: 5487679