fix(hosting): remove fullstack-branching and hosting pages re-added by #8624

[osama-rizk]

Description of changes:

Removes 10 pages that #8624 re-added by accident:

• src/pages/[platform]/deploy-and-host/fullstack-branching/** (9 files)
• src/pages/[platform]/deploy-and-host/hosting/index.mdx

#8605 moved these pages to deploy-and-host/amplify-hosting/ and added 301 redirects in redirects.json. #8624 ("Update amplify-js API references", merged from pre-prod/main) brought the old copies back. The child pages are byte-identical to their amplify-hosting/ counterparts.

The restored fullstack-branching/index.mdx isn't registered in directory.mjs, so getChildPageNodes returns [] and its <Overview> renders no cards. Each platform's build ends up with an empty page at a URL that's supposed to redirect.

No redirect changes are needed. The redirects from #8605 already cover every removed path.

Note: pre-prod/main still contains these files. They'll be removed there the next time main is merged into pre-prod/main.

Related GitHub issue #, if available:

Follow-up to #8605 / #8624.

Instructions

If this PR should not be merged upon approval for any reason, please submit as a DRAFT

Which product(s) are affected by this PR (if applicable)?

• amplify-cli
• amplify-ui
• amplify-studio
• amplify-hosting
• amplify-libraries

Which platform(s) are affected by this PR (if applicable)?

• JS
• Swift
• Android
• Flutter
• React Native

Please add the product(s)/platform(s) affected to the PR title

Checks

• Does this PR conform to the styleguide?

• Does this PR include filetypes other than markdown or images? Please add or update unit tests accordingly.

• Are any files being deleted with this PR? If so, have the needed redirects been created?

• Are all links in MDX files using the MDX link syntax rather than HTML link syntax?
  
  ref: MDX: [link](https://docs.amplify.aws/)
  HTML: <a href="https://docs.amplify.aws/">link</a>

When this PR is ready to merge, please check the box below

• Ready to merge

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mergify]

@osama-rizk, since a file was deleted from the src/pages and/or src/fragments directories, redirects might need to be set up so these previous pages do not 404. If redirects are needed, please answer these questions for each redirect that is needed:

• What is the source address of the redirect? (Where are you trying to redirect from?)

• What is the target address of the redirect? (Where are you trying to redirect to?)

• Type of redirect? 301 - permanent redirect or 302 - temporary redirect? (More info on Amplify Hosting redirects here: https://docs.aws.amazon.com/amplify/latest/userguide/redirects.html)

[mergify]

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