message: Removed deprecated Hasher alias from StringPiece.
  This will allow StringPiece to be replaced by an alias to absl::string_view.
diff: @@ -105,8 +105,6 @@ class StringPiece {
  StringPiece substr(size_t pos, size_t n = npos) const;
  - using Hasher = ::tensorflow::StringPieceHasher;
  -
  // Return a string that contains the copy of the referenced data.
  std::string ToString() const { return std::string(data_, size_); }
  