fix: remove event listeners on hydration error

[dummdidumm]

fixes #12360

While fixing this I realized this can happen for mount aswell. I really don't like all the additional code that is needed for this. Now I'm wondering if there's a better approach - for example, should teardown listeners be able to somehow run on error? Or is that a lost cause because we're in a broken state anyway?

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

🦋 Changeset detected

Latest commit: 16ddbc9

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[Rich-Harris]

there's a much simpler (and more comprehensive) fix! #12376