Remove references to the <Markdown> component

[matthewp]

What kind of changes does this PR include?

• New or updated content

Description

• Move the Markdown component to its own package astro#3986 removes the Markdown component from core, moves it to its own package.
• This removes documentation on the component. Docs are now in the package readme. We don't want to encourage people to use it anymore.

[netlify]

✅ Deploy Preview for astro-docs-2 ready!

Name	Link
🔨 Latest commit	f8564c1
🔍 Latest deploy log	https://app.netlify.com/sites/astro-docs-2/deploys/62dfd715dcd6bf000788267f
😎 Deploy Preview	https://deploy-preview-1045--astro-docs-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[hippotastic]

The more I think about the removal of the section ### <Markdown /> causing hard to resolve link issues in translated versions, the more I like your idea of leaving that section in there for now, @matthewp, but instead of hiding it, replacing the warning content with something along the lines of "This component is no longer built into Astro".

As soon as the translated pages that were previously referring to this component have been updated by the translators, we can then remove the section entirely in a second step (in a separate PR).

[delucis]

Love this fix and the green CI!

One note: we’ve just added an RC section in the migration guide, so we should probably also include a short note there saying something like

### `<Markdown />` Component Removed

If you were previously using Astro’s built-in `<Markdown />` component, this has been moved to a separate package. You will now need to install `@astrojs/markdown` and update your imports accordingly. For more details, see [the `@astrojs/markdown` README](...readme-link).

[sarah11918]

@matthewp I just updated the branch , so now this branch should have the latest migration guide with the RC changes section Chris is talking about.

There are already some items in there, so something like @delucis 's suggestion can be added to match the style and then... did we decide this is good to go now?? (LGTM re: proofreading)

[matthewp]

Updated with the suggested Migration note.

[sarah11918]

Thanks @matthewp !

@delucis , I'm assuming that this @astrojs/markdown component does NOT get automatically added to our Integrations page?

• Do we want a legacy package on our integrations page, so that we don't need to send people externally to the README but can instead have a page in Docs? Or, do we specifically NOT want this showing up in Docs, because we don't want people using it unless they really have to?

• Do we want to take this opportunity here in the migration guide to encourage people to transition to MDX, or simply say, "Here's where the new package is?"

[matthewp]

I think we don't want people using it unless they really have to.

Agree that it's a good opportunity to push people towards MDX, I'll add that.