Hide unwanted sublabel on Clear on Exit toggle button

[emerick]

Resolves brave/brave-browser#28269

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• 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/Custom-Headers
  • 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:

[mkarolin]

LGTM

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[stephendonner]

Verified PASSED using

Brave	1.50.9 Chromium: 110.0.5481.77 (Official Build) nightly (x86_64)
Revision	65ed616c6e8ee3fe0ad64fe83796c020644d42af-refs/branch-heads/5481@{#839}
OS	macOS Version 11.7.3 (Build 20G1116)

Steps:

1. installed 1.50.9
2. launched Brave
3. opened brave://settings/cookies
4. looked at the Clear cookies and site data when you close all windows pref

Confirmed there no longer is the (literal) subtext of When on, you'll also be signed out of Brave.

1.50.9	1.48.152

[kjozwiak]

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

Brave | 1.50.11 Chromium: 110.0.5481.77 (Official Build) nightly (64-bit)
-- | --
Revision | 65ed616c6e8ee3fe0ad64fe83796c020644d42af-refs/branch-heads/5481@{#839}
OS | Windows 11 Version 22H2 (Build 22621.1194)

1.50.6 Chromium: 110.0.5481.77	1.50.11 Chromium: 110.0.5481.77