ERC721 transfer should not emit Approval event

[AnAllergyToAnalogy]

As per the ERC721 standard, the Approval event should not be emitted on token transfer. It is implicit in the emitted Transfer event.

    /// @dev This emits when the approved address for an NFT is changed or
    ///  reaffirmed. The zero address indicates there is no approved address.
    ///  When a Transfer event emits, this also indicates that the approved
    ///  address for that NFT (if any) is reset to none.
    event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);

[k06a]

I think this discussion could be also related to the topic: makerdao/dss#76 and #1955

[AnAllergyToAnalogy]

Those discussions refer to ERC20, whereas this refers to ERC721. The ERC721 Standard is unambiguous about this, the Approval event shouldn't be emitting on a transfer.

[Amxx]

You opened this PR twice.

Please lets only keep one instance opened #3483