message: Fix VLA error in hash.h
  Prior updates to the build system now treat VLAs as errors, so we need
  to fix `src/hash.h`
diff: @@ -39,9 +39,9 @@ public:
  void Finalize(unsigned char hash[OUTPUT_SIZE])
  {
  - unsigned char buf[sha.OUTPUT_SIZE];
  + unsigned char buf[CSHA256::OUTPUT_SIZE];
  sha.Finalize(buf);
  - sha.Reset().Write(buf, sha.OUTPUT_SIZE).Finalize(hash);
  + sha.Reset().Write(buf, CSHA256::OUTPUT_SIZE).Finalize(hash);
  }
  CHash256& Write(const unsigned char* data, size_t len)
  @@ -99,9 +99,9 @@ public:
  void Finalize(unsigned char hash[OUTPUT_SIZE])
  {
  - unsigned char buf[sha.OUTPUT_SIZE];
  + unsigned char buf[CSHA256::OUTPUT_SIZE];
  sha.Finalize(buf);
  - CRIPEMD160().Write(buf, sha.OUTPUT_SIZE).Finalize(hash);
  + CRIPEMD160().Write(buf, CSHA256::OUTPUT_SIZE).Finalize(hash);
  }
  CHash160& Write(const unsigned char* data, size_t len)
  