Remove first-time indexation notice from Indexation.js and FTC indexation.js

[JSCHLTE]

Context

This PR removes the outdated first-time indexation notice from the plugin’s UI. The message previously referenced legacy features (Text Link Counter and Internal Linking Analysis) which have since been merged into the core indexation process.

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Summary

Changelog label: changelog: non-user-facing

This PR can be summarized in the following changelog entry:

• Removes the first-time indexation notice from Indexation.js and the First Time Configuration flow.

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Relevant technical choices:

• Deleted the renderFirstIndexationNotice() method in Indexation.js
• Removed its conditional rendering
• Ensured no duplicates existed in FTC's indexation.js
• Verified yarn build and yarn lint passed for only the edited files

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Test instructions

Acceptance testing steps:

1. Run yarn build — it should succeed without errors related to these files.
2. Run yarn lint — your changes should pass without CRLF errors.
3. Confirm the following message is no longer shown:

   "This feature includes and replaces the Text Link Counter and Internal Linking Analysis"

4. Check the First Time Configuration screen and Tools page — the notice should not appear.
5. Check that no React or console errors appear due to missing method references.

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Relevant test scenarios

• Changes should be tested with the browser console open
• Changes are JS-only — not post-type dependent
• No editor integrations are affected
• Browser-agnostic (React logic only)
• Multisite not relevant

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Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

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Impact check

This PR touches the indexation UI in both the Tools screen and FTC flow. It should be tested in both places to ensure the notice is gone and no JS errors occur from removed methods.

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UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

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Other environments

• Not applicable to Shopify

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Documentation

• Covered by inline comments and clear PR description

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Quality assurance

• I have tested this code to the best of my abilities.
• I have run yarn build and yarn lint.
• I have verified the base branch is trunk.

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Innovation

• No innovation project is applicable for this PR.

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Fixes #21689