message: doc: remove outdated comment
  No longer relevant because Boost 1.46 is no longer supported and
  std::unordered_map is used instead of boost::unordered_map in CCoinsMap.
diff: @@ -33,10 +33,6 @@ public:
  SaltedOutpointHasher();
  /**
  - * This *must* return size_t. With Boost 1.46 on 32-bit systems the
  - * unordered_map will behave unpredictably if the custom hasher returns a
  - * uint64_t, resulting in failures when syncing the chain (#4634).
  - *
  * Having the hash noexcept allows libstdc++'s unordered_map to recalculate
  * the hash during rehash, so it does not have to cache the value. This
  * reduces node's memory by sizeof(size_t). The required recalculation has
  