fix sync error when default newtab site is visited

[diracdeltas]

fix #8217 and refactors syncUtil/urlBarSuggestions to use common siteUtil methods

Test Plan:

1. enable sync in a clean profile
2. go to https://brave.com
3. you should not see any console errors

• 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).
• Ran git rebase -i to squash commits (if needed).

Test Plan:

[ayumi]

test plan works
tests pass
sweet

yarn test -- --grep='"'^Sync'"'