Simplify accumulator refreshes

Passed Non-Regression STC:
https://tests.stockfishchess.org/tests/view/6631f5d5d01fb9ac9bcdc7d0
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 57472 W: 14979 L: 14784 D: 27709
Ptnml(0-2): 185, 6486, 15192, 6695, 178

closes #5207

No functional change

src/nnue/nnue_feature_transformer.h

@@ -668,20 +668,20 @@ class FeatureTransformer {
             for (IndexType k = 0; k < NumRegs; ++k)
                 acc[k] = entryTile[k];
 
-            int i0 = 0;
-            for (; i0 < int(std::min(removed.size(), added.size())); ++i0)
+            int i = 0;
+            for (; i < int(std::min(removed.size(), added.size())); ++i)
             {
-                IndexType       indexR  = removed[i0];
+                IndexType       indexR  = removed[i];
                 const IndexType offsetR = HalfDimensions * indexR + j * TileHeight;
                 auto            columnR = reinterpret_cast<const vec_t*>(&weights[offsetR]);
-                IndexType       indexA  = added[i0];
+                IndexType       indexA  = added[i];
                 const IndexType offsetA = HalfDimensions * indexA + j * TileHeight;
                 auto            columnA = reinterpret_cast<const vec_t*>(&weights[offsetA]);
 
                 for (unsigned k = 0; k < NumRegs; ++k)
                     acc[k] = vec_add_16(vec_sub_16(acc[k], columnR[k]), columnA[k]);
             }
-            for (int i = i0; i < int(removed.size()); ++i)
+            for (; i < int(removed.size()); ++i)
             {
                 IndexType       index  = removed[i];
                 const IndexType offset = HalfDimensions * index + j * TileHeight;
@@ -690,7 +690,7 @@ class FeatureTransformer {
                 for (unsigned k = 0; k < NumRegs; ++k)
                     acc[k] = vec_sub_16(acc[k], column[k]);
             }
-            for (int i = i0; i < int(added.size()); ++i)
+            for (; i < int(added.size()); ++i)
             {
                 IndexType       index  = added[i];
                 const IndexType offset = HalfDimensions * index + j * TileHeight;