Remove failedLow from the mainThread struct

failedLow is in fact a local variable in Thread::search().

Also clean some spaces and tabs in code.

No functional change.

src/pawns.cpp

@@ -34,7 +34,7 @@ namespace {
   // Pawn penalties
   constexpr Score Isolated = S(13, 16);
   constexpr Score Backward = S(17, 11);
-  constexpr Score Doubled = S(13, 40);
+  constexpr Score Doubled  = S(13, 40);
 
   // Connected pawn bonus by opposed, phalanx, #support and rank
   Score Connected[2][2][3][RANK_NB];