Fix incorrect comment in EIP-3448 implementation

[T1MOH593]

This comment defines deploy code size:

  function _metaProxyFromMemory (address targetContract, uint256 offset, uint256 length) internal returns (address addr) {
    ...
@>    // The size is deploy code + contract code + calldatasize - 4 + 32.
      addr := create(0, start, sub(ptr, start))
    }
  }

Struggled some time to figure out what is calldata in this context. Eventually this comment was copied from previous function where it used the whole calldata except 4 bytes selector.

PR proposes right comment because length exactly defines metadata length.

[eip-review-bot]

File ERCS/erc-3448.md

Requires 1 more reviewers from @axic, @g11tech, @gcolvin, @lightclient, @samwilsn, @xinbenlv

[SamWilsn]

Would be ideal to get a review from @pinkiebell (as the author.)