Remove outdated SDK link files

It appears that this was mistakenly left behind when the site was redesigned in modelcontextprotocol#1044.

The `<Card>` components containing the link information for each SDK are defined in the `docs/docs/sdk.mdx` file:
https://github.com/modelcontextprotocol/modelcontextprotocol/blob/0695a49/docs/docs/sdk.mdx

So the `.mdx` files under the `docs/links/sdks` directory no longer seem necessary.

Author: koic