Remove PSQT-only mode

Passed STC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 94208 W: 24270 L: 24112 D: 45826
Ptnml(0-2): 286, 11186, 24009, 11330, 293
https://tests.stockfishchess.org/tests/view/6635ddd773559a8aa8582826

Passed LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 114960 W: 29107 L: 28982 D: 56871
Ptnml(0-2): 37, 12683, 31924, 12790, 46
https://tests.stockfishchess.org/tests/view/663604a973559a8aa85881ed

closes #5214

Bench 1653939

src/nnue/nnue_accumulator.h

@@ -38,7 +38,6 @@ struct alignas(CacheLineSize) Accumulator {
     std::int16_t accumulation[COLOR_NB][Size];
     std::int32_t psqtAccumulation[COLOR_NB][PSQTBuckets];
     bool         computed[COLOR_NB];
-    bool         computedPSQT[COLOR_NB];
 };
 
 
@@ -63,7 +62,6 @@ struct AccumulatorCaches {
             PSQTWeightType psqtAccumulation[PSQTBuckets];
             Bitboard       byColorBB[COLOR_NB];
             Bitboard       byTypeBB[PIECE_TYPE_NB];
-            bool           psqtOnly;
 
             // To initialize a refresh entry, we set all its bitboards empty,
             // so we put the biases in the accumulation, without any weights on top