Force the referrer to always be 'no-referrer' while in speedreader mode.

[boocmp]

Resolves brave/brave-browser#35095

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

1. Visit https://secret-subdomain.csrf.jp/2024/brave-speedreader-meta-referrer-bypass.php
2. Push memo icon in the address bar and open the page with Speedreader
3. Click the link "Referrer Check"
4. Check that the secret domain name (secret-subdomain.csrf.jp) isn't sent to the evil website through REFERER header

[kjozwiak]

Verification PASSED on Win 11 x64 using the following build(s):

Brave | 1.63.97 Chromium: 120.0.6099.199 (Official Build) nightly (64-bit)
-- | --
Revision | 3422bfceaa2c9ed3cdc478c9e7009893c7078a3b
OS | Windows 11 Version 22H2 (Build 22621.2861)

Reproduced the original on 1.63.92 Chromium: 120.0.6099.144 using the STR/Cases outlined via #21481 (comment). Once reproduced, used the same STR/Cases and ensured that the issue has been fixed via 1.63.97 Chromium: 120.0.6099.199 as per the following:

Example	Example