Use standard Promise.allSettled instead polyfill

[outsideris]

Description of the Change

We've introduced @ungap/promise-all-settled in #4476.
And Node.js support Promise.allSettled in Node 12.9.0.

So, we don't need polyfill anymore because we support Node 14+.

Why should this be in core?

We don't need polyfill anymore.

Benefits

dependency is reduced.

Possible Drawbacks

N/A

[coveralls]

Coverage decreased (-0.002%) to 94.326% when pulling c557d79 on use-builtin-allsettled into 84b2f84 on master.

[juergba]

@outsideris I guess this PR makes sense.
One of your links points to a korean page. I couldn't find any docs about Node supporting Promise.allSettled(). Can you help, please?

[outsideris]

Oops! Sorry for korea link.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/allSettled

And you can see 12.9.0 release note.

[juergba]

@outsideris thank you for your explanations and this PR.