chore: remove svelte-migrate from readme

[manuel3108]

Relates: #1124 (comment)

Description

Checklist

• Update snapshots (if applicable)
• Add a changeset (if applicable)
• Allow maintainers to edit this PR
• I care about what I'm doing, no matter the tool I use (Notepad, Sublime, VSCode, AI...)

[pkg-svelte-dev]

Install the latest version of sv from 13721a0:

pnpm add https://pkg.svelte.dev/sv/c/13721a061342ec9ee9c118ed249fac5e99d6898e

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/cli/pr/1221

[changeset-bot]

⚠️ No Changeset found

Latest commit: 13721a0

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

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-cli-1221-svelte.vercel.app/