[Cr99 follow up] Account for changes to WebUI JS code naming to reflect the Profile::IsChild API

[mkarolin]

Fixes brave/brave-browser#21225

Needed to rename isSupervised to isChildAccount to match upstream. Bug
manifested itself as missing settings for "Clear on Exit" and an error in the
JavaScript console.

Chromium change:

https://source.chromium.org/chromium/chromium/src/+/5441f9b71eecac1b8acfafa78dbc7c4148cb2143

commit 5441f9b71eecac1b8acfafa78dbc7c4148cb2143
Author: Nohemi Fernandez fernandex@chromium.org
Date: Tue Dec 14 13:11:35 2021 +0000

Update WebUI JS code naming to reflect the Profile::IsChild API.

Follow-up to crrev.com/c/3314914.

Bug: 1277015

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, npm run lint, 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:

[mariospr]

++

[mkarolin]

Windows CI is failing on dist-deltas, which is unrelated to this PR.