Remove QS_CHECKS movepick stage

Passed STC: https://tests.stockfishchess.org/tests/view/669597cf4ff211be9d4ec147
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 199072 W: 52100 L: 52058 D: 94914
Ptnml(0-2): 829, 23679, 50406, 23865, 757

Passed LTC: https://tests.stockfishchess.org/tests/view/66988f5f4ff211be9d4ec33e
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 119778 W: 30420 L: 30299 D: 59059
Ptnml(0-2): 106, 13293, 32957, 13440, 93

closes https://github.com/official-stockfish/Stockfish/pull/5498

Bench 1499842

src/types.h

@@ -194,8 +194,7 @@ enum : int {
     // quiescence search, however, the transposition table entries only store
     // the current quiescence move generation stage (which should thus compare
     // lower than any regular search depth).
-    DEPTH_QS_CHECKS = 0,
-    DEPTH_QS_NORMAL = -1,
+    DEPTH_QS = 0,
     // For transposition table entries where no searching at all was done
     // (whether regular or qsearch) we use DEPTH_UNSEARCHED, which should thus
     // compare lower than any quiescence or regular depth. DEPTH_ENTRY_OFFSET