Calling `abort` multiple times causes the `abort` event to be triggered multiple times

This is not how it's supposed to work.

```js
const { AbortController } = require('abortcontroller-polyfill/dist/cjs-ponyfill');

const a = new AbortController()
a.signal.addEventListener('abort', () => console.log('aborted'))
a.abort()
a.abort()

// outputs "aborted" twice
```