message: Remove unused variable.
  Detected by the new compile-clang CI stage, so this unbreaks
  the build.
diff: @@ -68,10 +68,6 @@ using verible::ValueSaver;
  static constexpr AlignmentColumnProperties FlushLeft(true);
  static constexpr AlignmentColumnProperties FlushRight(false);
  -// Special SyntaxTreePath index used for non-tree tokens
  -static const SyntaxTreePath::value_type kNonTreeTokenPathIndex =
  - std::numeric_limits<SyntaxTreePath::value_type>::max();
  -
  static const SyntaxTreePath::value_type kLeadingNonTreeTokenPathIndex = -1;
  static const SyntaxTreePath::value_type kTrailingNonTreeTokenPathIndex =
  std::numeric_limits<SyntaxTreePath::value_type>::max();
  