Use simple loop for longestCommonPrefixPartialKey

The benchmark has this as faster

ConflictSet.cpp

@@ -720,42 +720,13 @@ bytes:
 
 int longestCommonPrefixPartialKey(const uint8_t *ap, const uint8_t *bp,
                                   int cl) {
-  if (cl > Node::kPartialKeyMaxLen) {
-    __builtin_unreachable(); // GCOVR_EXCL_LINE
-  }
-  return longestCommonPrefix(ap, bp, cl);
-#if 0
-static_assert(Node::kPartialKeyMaxLen == 16);
-  // SOMEDAY: use masked loads (requires avx-512/sve2)
-#if defined(HAS_AVX)
-  __m128i a;
-  memcpy(&a, ap, cl);
-  __m128i b;
-  memcpy(&b, bp, cl);
-  const auto compared = _mm_cmpeq_epi8(a, b);
-  int mask = (1 << cl) - 1;
-  auto c = = _mm_movemask_epi8(compared) & mask;
-  return std::countr_zero(~c);
-#elif defined(HAS_ARM_NEON)
-  uint8x16_t a;
-  memcpy(&a, ap, cl);
-  uint8x16_t b;
-  memcpy(&b, bp, cl);
-  uint16x8_t results = vreinterpretq_u16_u8(vceqq_u8(a, b));
-  uint64_t mask = cl == 16 ? uint64_t(-1) : (uint64_t(1) << (cl * 4)) - 1;
-  uint64_t bitfield =
-      vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(results, 4)), 0) & mask;
-  return std::countr_zero(~bitfield) >> 2;
-#else
   int i = 0;
-  for (; i < 16; ++i) {
+  for (; i < cl; ++i) {
     if (*ap++ != *bp++) {
       break;
     }
   }
   return i;
-#endif
-#endif
 }
 
 // Performs a physical search for remaining