Eliminate regenerator from preset-react-app plugins

[conartist6]

Regenerator is already included by preset-env.

Fixes #4627

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[Timer]

This broke CI so I don't think we can make this change safely.

[conartist6]

@Timer when you say "this broke CI" could you point me to the failure so that I could attempt to understand what broke and why? It is, unfortunately, also not safe not to make this change, as the bug if fixes is "syntactically correct code can't be compiled".

[gaearon]

@conartist6 Which bug does this fix? Thanks!

[gaearon]

Oops sorry, I missed your link. Can you rebase and then we re-run it? We'd need a regression test to understand what you were fixing too.

[conartist6]

Certainly, I'll write the test and rebase the branch.

[gaearon]

Seems like it passes now. So maybe it was transient.
In either case we'd need a new integration test for the case that was broken.

[conartist6]

That makes sense, CI was broken for every single PR at the time when I first opened this.

[conartist6]

@Timer Could you please explain?

[Timer]

GitHub doesn't like when you delete a branch that has PRs against it. 😅