[1.3] Hide sync menu from app menu if it's disabled

[simonhong]

and fix failed app menu test.

fix brave/brave-browser#8160
fix brave/brave-browser#8158 (only for 1.3)

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
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• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
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• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• Public documentation has been updated as necessary. 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-Protection-Mode
  • 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-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

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.

[simonhong]

Pushed different PR for fix this issue because brave app menu code was refactored from 1.4.
#4571 could be uplifted from 1.6 to 1.4 if needed.

[simonhong]

Only network-audit and test-install were failed in CI. and it seems both are not related with this PR.

[kjozwiak]

Uplift into 1.3.x after deliberating with @brave/uplift-approvers. As per #4570 (comment), looks like audit-network and test-install failed which are expected failures and not related to this specific PR.

Please make sure that the correct labels are being used and the associated issue is moved into the correct milestone.