message: get rid of uint256 struct that snuck its way back in via merges
diff: @@ -28,26 +28,6 @@ using field_name = fixed_string16;
  using table_name = name;
  using action_name = eosio::chain::action_name;
  -// Must be in sync with definition in contracts/eoslib
  -struct uint256 {
  - uint64_t words[4];
  -
  - uint256()
  - {
  - for( auto i = 0; i < 4; ++i )
  - words[i] = 0;
  - }
  -
  - bool operator<(const uint256& other)const {
  - for( auto i = 0; i < 4; ++i )
  - {
  - if( words[i] < other.words[i] ) return true;
  - else if( words[i] > other.words[i] ) return false;
  - }
  - return false;
  - }
  -};
  -
  struct type_def {
  type_def() = default;
  type_def(const type_name& new_type_name, const type_name& type)
  