Removed unreachable Results.prototype.only code

[taylorhakes]

I was looking though the results.js file and noticed invalid code.

if (this._only) {
  self.count ++;
  self.fail ++;
  write('not ok ' + self.count + ' already called .only()\n');
}

self and write are not defined. I tried to write a failing test, but found out that the code was unreachable because there is a similar check in index.js before reaching this code.

if (only) throw new Error('there can only be one only test');
results.only(name);

This pull requests removes the broken unreachable code. I also added a test for duplicate test.only calls.

[Raynos]

Thanks for this bugfix :)

[Raynos]

Published v4.4.0