Remove widget promo

[deeppandya]

Resolves brave/brave-browser#30618

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 wiki
  • npm run lint, npm run presubmit wiki, 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:

[samartnik]

lgtm

[SergeyZhukovsky]

++

[kjozwiak]

Verification PASSED on Pixel 6 running Android 14 using the following build(s):

Brave | 1.54.16 Chromium: 114.0.5735.53 (Official Build) canary (64-bit)
--- | ---
Revision | c499d7ea22c8b2dba278465a5df7b86a8efa4e64-refs/branch-heads/5735@{#970}
OS | Android 13; Build/UPB2.230407.014; 33; UpsideDownCake

Test Case #1 (opening tabs/restarting browser)

• opened ~30 tabs and ensured that the OSK is being shown when tapping on the omnibox every single time
  • ensured that the Widget onboarding modal isn't triggered/appearing when tapping on the omnibox
  • after opening ~30 different tabs, restart the browser ~20 times and ensured that the Widget onboarding isn't displayed
  • ensured that you can still add a home widget via Hambruger Menu -> Settings -> Home screen widget
    • ensured that you can add other Brave widgets via Widgets on the Android Home screen
• ensured that all the widgets are removed when Brave is uninstalled

Test Case #2 (restarting browser/opening tabs)

• opened Brave ~30 times and ensured that the OSK is being shown when tapping on the omnibox every single time
  • ensured that the Widget onboarding modal isn't triggered/appearing when tapping on the omnibox
  • after opening Brave ~30 different times, opened ~20 tabs and ensured that the Widget onboarding isn't displayed
  • ensured that you can still add a home widget via Hambruger Menu -> Settings -> Home screen widget
    • ensured that you can add other Brave widgets via Widgets on the Android Home screen
• ensured that all the widgets are removed when Brave is uninstalled