chore(api): remove index.html page from Sphinx docs build (#19121)

# Overview

Removing the `index.html` page from our Sphinx docs build. This page
only served as a redirect to `docs.opentrons.com/v2`. Once we launch our
mkdocs site, it will provide an index page that serves as a portal to
all our docs publications.

## Test Plan and Hands on Testing

- My first commit on this branch still included
`api/docs/dist/index.html` so that got synced to the sandbox.
- Subsequent commit removed it, but our sync isn't deleting files. So it
remained.
- Created a new branch `docs-remove-redirect-new` that has identical
commits to this one and ran the API docs action. It has no index.html
page and the rest of the site (within `v2/`) looks correct.
<img width="2438" height="1010" alt="Screenshot 2025-08-05 at 12 02
11 PM"
src="https://github.com/user-attachments/assets/59bedf7e-238f-49a1-8728-716c75d49ce7"
/>

![mission-failed-successfully](https://github.com/user-attachments/assets/e2d43cb7-d4a9-4df5-a2e3-df8c8b9e9441)

I'm guessing this means we should change the sync behavior? We need to
make sure that it is scoped to only `v1/`, `v2/`, `ot1/`, and
`hardware/` so it doesn't clobber mkdocs sites synced by other actions.

## Changelog

Remove a couple files.

## Review requests

Seems right?

## Risk assessment

pretty low

Author: ecormany