docs: simplify $effect.tracking() docs

[Rich-Harris]

while reviewing #14821, I realised that the $effect.tracking() docs come across a bit strangely now that we have createSubscriber. I think it makes more sense to just link to those docs to explain the purpose of the rune, rather than laboriously recreating a worse version of the abstraction (which someone might, seeing those docs, decide to use).

It also means that we're spending less real estate on an extremely niche feature that most people shouldn't be touching

[changeset-bot]

⚠️ No Changeset found

Latest commit: 9ec8601

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

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

[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14939-svelte.vercel.app/

this is an automated message

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14939