Sync don't do double reset

[AlexeyBarabash]

Fix brave/brave-browser#3188 .
Fix brave/brave-browser#3225 .

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
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux

1 test crashed:
    BraveSchemeLoadBrowserTest.NotAllowedToBraveFromChrome

• 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:

Taken from brave/brave-browser#3188

Devices
Device 1: Samsung Tab running 1.0.76
Device 2: Pixel 3XL running 1.0.76
Device 3: Linux running 0.59.34 profile 1 (Sync already created and reset)
Device 4: Linux running 0.59.34 profile 2

Steps to Reproduce

1. Create bookmarks and folders on device 1
2. Create sync chain on Device 1 and scan QR code on device 2, ensure all bookmarks are sync'd on device2
3. Reset existing sync on device 3 which has existing bookmarks
4. Enter code words from device 1 and join device 3 on the sync chain, bookmarks from device 1 sync on device 3
5. Existing bookmarks from device 3 isn't sync'd to device 1 or device 2
6. Create bookmarks on device 4 and join the sync chain using code words
7. Once device is listed, device 4 sync's all bookmarks from device 1, similarly device 1,2 & 3 sync's all bookmarks from device 4

Taken from brave/brave-browser#3225

Steps to Reproduce

1. Create sync chain brave-core device1
2. Connect to sync chain brave-core device2
3. Create bookmark on device1 and ensure it is synced to device2
4. On device1 press View sync code -> View QR code, do the screenshot of QR code
5. On device2 press Leave Sync Chain
6. Wait until both devices will get sync turned off
7. With the Android device connect to existing sync chain with QR at pt 4

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

[AlexeyBarabash]

Updated first message with issue for zombies brave/brave-browser#3225 .

[darkdh]

lgtm. please squash some commits if necessary.

[AlexeyBarabash]

@darkdh
squashed some commits. could you please look again.