Outpost array simplification

The ReachableOutpost values were almost exactly half the Outpost values.

Passed STC
http://tests.stockfishchess.org/tests/view/588020510ebc5915193f781e
LLR: 3.86 (-2.94,2.94) [-3.00,1.00]
Total: 119238 W: 21462 L: 21460 D: 76316

Passed LTC
http://tests.stockfishchess.org/tests/view/5880ae090ebc5915193f7843
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 23540 W: 3097 L: 2980 D: 17463

Curiously, using a division by 2, with slightly different values, did not passed
http://tests.stockfishchess.org/tests/view/587fece00ebc5915193f780a

bench: 5828283