[Vis Tools] Delete old, old Timeline Tool

[juliawu]

This PR removes the codepaths that supported the old, un-revamped /tools/timeline UI.

Summary

Now that the "standardized_vis_tool" experience is the default experience, this PR removes the old /tools/timeline experience so that we can eventually delete the flag. In order to keep changes concise, I've only removed the old /tools/timeline in this PR. Removing /tools/visualization will come in a separate PR.

Related PRs:
/tools/map is being removed in #6165
/tools/scatter is being removed in #6167

Testing Strategy

Locally, I set the "standardized_vis_tool" flag to False, and verified that:

• navigating to localhost:8080/tools/timeline still renders the new, standardized experience.
• webdriver, client, and python tests still pass

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request completes the transition to the standardized visualization tool for the timeline page by removing all legacy code paths and UI components. By making the standardized experience the default and only implementation, this change simplifies the codebase and prepares for the eventual removal of associated feature flags.

Highlights

• Removal of Legacy Timeline UI: Removed all code paths, templates, and configurations associated with the old, un-revamped /tools/timeline UI, standardizing on the new visualization tool experience.
• Test Suite Cleanup: Updated webdriver tests to remove legacy test mixins and feature flag-based test cases, ensuring the test suite now only validates the standardized timeline experience.

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[gemini-code-assist]

Code Review

This pull request removes the feature flag for the standardized timeline tool, making it the permanent UI. The changes include simplifying the backend route in html.py, updating the Jinja2 template, deleting the legacy info.tsx component, and refactoring the React Page component to remove conditional logic. Additionally, the WebDriver tests have been consolidated to reflect the removal of the old UI. I have no feedback to provide as there were no review comments to evaluate.

[nick-nlb]

LGTM