Don't emit Approval event when approval is cleared on transfer (#1038)

[abandeali1]

Fixes #1038

🚀 Description

See title.

• 📘 I've reviewed the OpenZeppelin Contributor Guidelines
• ✅ I've added tests where applicable to test my new functionality.
• 📖 I've made sure that my contracts are well-documented.
• 🎨 I've run the JS/Solidity linters and fixed any issues (npm run lint:all:fix).

[shrugs]

LGTM

[johnhforrest]

Not opening a new PR for this one, but noticed that this block can be cleaned up when I was porting this over to our repo:

if (approved) {
  it('emit only a transfer event', async function () {
    logs.length.should.be.equal(1);
    logs[0].event.should.be.eq('Transfer');
    logs[0].args._from.should.be.equal(owner);
    logs[0].args._to.should.be.equal(this.to);
    logs[0].args._tokenId.should.be.bignumber.equal(tokenId);
    });
  } else {
    it('emits only a transfer event', async function () {
      logs.length.should.be.equal(1);
      logs[0].event.should.be.eq('Transfer');
      logs[0].args._from.should.be.equal(owner);
      logs[0].args._to.should.be.equal(this.to);
      logs[0].args._tokenId.should.be.bignumber.equal(tokenId);
    });
  }