Use score instead of array to evaluate shelter

This is a non-functional simplification. Instead of an array of values, just use a Score.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 16309 W: 3673 L: 3541 D: 9095
http://tests.stockfishchess.org/tests/view/5d24f3b80ebc5925cf0ceb5b

No functional change

src/search.cpp

@@ -1070,7 +1070,7 @@ moves_loop: // When in check, search starts from here
           Depth r = reduction(improving, depth, moveCount);
 
           // Reduction if other threads are searching this position.
-	  if (th.marked())
+          if (th.marked())
               r += ONE_PLY;
 
           // Decrease reduction if position is or has been on the PV