Simplify using previous PV along the first PV line

Non-regression STC:
LLR:  2.94/2.94<-6.00, 0.00> Elo diff: 2.46 [-1.31, 6.23] (95%)
Games: 7201 W: 877 L: 826 D: 5498 Draw ratio: 76.4%
Pntl: [33, 632, 2225, 671, 39]

Non-regression LTC:
LLR:  2.98/2.94<-6.00, 0.00> Elo diff: 0.14 [-1.88, 2.15] (95%)
Games: 17907 W: 1470 L: 1462 D: 14975 Draw ratio: 83.6%
Pntl: [42, 1217, 6439, 1202, 53]

Bench: 1828256

src/Search.cpp

@@ -511,7 +511,7 @@ namespace Search
         Move best_move = MOVE_NULL;
         Move quiet_list[NUM_MAX_MOVES];
         MoveList quiets_searched(quiet_list);
-        Move hash_move = (data.in_pv() && data.pv_move() != MOVE_NULL) ? data.pv_move() : tt_move;
+        Move hash_move = (RootSearch && data.pv_move() != MOVE_NULL) ? data.pv_move() : tt_move;
         MoveOrder orderer = MoveOrder(position, depth, hash_move, history);
         while ((move = orderer.next_move()) != MOVE_NULL)
         {