Remove unused Rails views and init files

What does this MR do and why?

Since we've moved to using Vue router for self-hosted models page navigation, some Rails views and init files are now redundant and can be removed.

• Removes Self-hosted models new HAML view and frontend init file
• Removes Self-hosted models edit HAML view (the init file was removed in this MR but the view was accidentally missed)

References

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MR acceptance checklist

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Before	After

How to set up and validate locally

Prequisites

You will need an active GitLab ultimate license.

1. Start GDK instance in self-managed mode:

GITLAB_SIMULATE_SAAS=0 && gdk start

2. Visit the GDK feature flags page and ensure the following flags are enabled ai_custom_model
3. Go to the rails console and ensure Code Suggestions is enabled

ApplicationSetting.first.update(duo_features_enabled: true)

Test it!

1. Log in as an admin
2. Visit Admin Area > Self-hosted models

3. Ensure self-hosted models routing functionality is working as expected:

• Self-hosted models can be created, edited, deleted as usual