[WIP] refactor: remove useNewCourseOutlinePage flag from textbooks breadcrumb

[farhan]

Description

Describe what this pull request changes, and why. Include implications for people using this change.
Design decisions and their rationales should be documented in the repo (docstring / ADR), per
OEP-19, and can be linked here.

Useful information to include:

• Which user roles will this change impact? Common user roles are "Learner", "Course Author",
  "Developer", and "Operator".
• Include screenshots for changes to the UI (ideally, both "before" and "after" screenshots, if applicable).

Supporting information

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Be sure to check they are publicly readable, or if not, repeat the information here.

Testing instructions

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Other information

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• Does this change depend on other changes elsewhere?
• Any special concerns or limitations? For example: deprecations, migrations, security, or accessibility.

Best Practices Checklist

We're trying to move away from some deprecated patterns in this codebase. Please
check if your PR meets these recommendations before asking for a review:

• Any new files are using TypeScript (.ts, .tsx).
• Avoid propTypes and defaultProps in any new or modified code.
• Tests should use the helpers in src/testUtils.tsx (specifically initializeMocks)
• Do not add new fields to the Redux state/store. Use React Context to share state among multiple components.
• Use React Query to load data from REST APIs. See any apiHooks.ts in this repo for examples.
• All new i18n messages in messages.ts files have a description for translators to use.
• Avoid using ../ in import paths. To import from parent folders, use @src, e.g. import { initializeMocks } from '@src/testUtils'; instead of from '../../../../testUtils'

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.55%. Comparing base (36d42b0) to head (4a061ec).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3067   +/-   ##
=======================================
  Coverage   95.55%   95.55%           
=======================================
  Files        1393     1393           
  Lines       32992    32979   -13     
  Branches     7644     7654   +10     
=======================================
- Hits        31524    31514   -10     
+ Misses       1413     1399   -14     
- Partials       55       66   +11     

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[bradenmacdonald]

Let me know when you'd like me to review this :)