Remove unused field

ConflictSet.cpp

@@ -790,7 +790,6 @@ struct ReadContext {
   int64_t commits_accum = 0;
   int64_t conflicts_accum = 0;
   int64_t too_olds_accum = 0;
-  ConflictSet::Impl *impl;
   bool operator==(const ReadContext &) const = default; // GCOVR_EXCL_LINE
 };
 
@@ -4808,7 +4807,6 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
 
     int64_t check_byte_accum = 0;
     check::Context context;
-    context.readContext.impl = this;
 
     if constexpr (kEnableInterleaved) {
       if (count == 1) {
@@ -4844,7 +4842,6 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
         Arena arena;
         auto *results2 = new (arena) Result[count];
         check::Context context2;
-        context2.readContext.impl = this;
         useSequential(reads, results2, count, context2);
         assert(memcmp(result, results2, count) == 0);
         assert(context.readContext == context2.readContext);