fix(expect)!: fix toThrow("") behavior by reverting #6710

[hi-ogawa]

Description

• Related toThrowError() treats empty string param as though it is undefined #6618 (comment)

At that time, I thought this was a bug, but this special case behavior contradicts with doc https://main.vitest.dev/api/expect.html#tothrowerror. This PR essentially reverts #6710 to remove this behavior and follow the doc.

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[sheremet-va]

Isn't this a breaking change now?

[hi-ogawa]

I think so.

[sheremet-va]

As a note, jest also passes:

expect(() => {
  throw new Error('error')
}).toThrow('')