message: Remove the fingerprint() field from HloInstruction.
  It is more flexible to cache fingerprints in a separate hash table.
diff: @@ -1349,9 +1349,6 @@ class HloInstruction {
  const HloPrintOptions& options,
  CanonicalNameMap* canonical_name_map) const;
  - const absl::optional<uint64>& fingerprint() const { return fingerprint_; }
  - void set_fingerprint(const uint64 fingerprint) { fingerprint_ = fingerprint; }
  -
  // Returns a serialized representation of this instruction.
  virtual HloInstructionProto ToProto() const;
  @@ -2059,9 +2056,6 @@ class HloInstruction {
  // HloInstruction.
  bool IsMarkedAsDead() const { return marked_as_dead_; }
  - // Fingerprint of this instruction alone.
  - absl::optional<uint64> fingerprint_;
  -
  int unique_id_; // Unique to this HloInstruction within a HloModule
  // Opcode for this instruction.
  