message: libutils: fix inconsistent hash in StaticString
  This caused a unit test failure because a StaticString constructed
  from "make" had a different hash than one constructed from a literal,
  even though the two strings were lexigraphically equivalent.
diff: @@ -86,7 +86,7 @@ public:
  constexpr StaticString(StringLiteral<N> const& other) noexcept // NOLINT(google-explicit-constructor)
  : mString(other),
  mLength(size_type(N - 1)),
  - mHash(computeHash(other, N)) {
  + mHash(computeHash(other, N - 1)) {
  // we rely on inlining for computeHash. It would be nice to do this with constexpr
  // instead, but unfortunately 'other' is not constexpr once a parameter.
  }
  @@ -98,7 +98,7 @@ public:
  mLength = size_type(N - 1);
  // we rely on inlining for computeHash. It would be nice to do this with constexpr
  // instead, but unfortunately 'other' is not constexpr once a parameter.
  - mHash = computeHash(other, N);
  + mHash = computeHash(other, N - 1);
  return *this;
  }
  