Uplift to 0.61.x of #1643, Sync revert network connection tracker

[AlexeyBarabash]

Uplift into 0.61.x of #1643, Sync revert network connection tracker

Fix brave/brave-browser#3278 .

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) - removed some tests.
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux
• 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

Test Plan:

1. Disable network connection
2. Run brave-core
3. Open brave://sync
4. Press Start a new Sync chain => Computer
5. Should see more general error
   

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

[bbondy]

Deferring decision on this to @darkdh