[HangoutsExtension] Remove hangouts extension

[jagadeshjai]

• Disable hangouts extension by passing the buildflag via GN args.
• Remove the option available for the same in setting page.

Resolves brave/brave-browser#39660

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• 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 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/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

Upgrade scenario

Snippet courtesy of https://fedi.simonwillison.net/@simon/112757810519145581

1. Have a version of Brave BEFORE this change - clean profile.
2. Visit brave://settings/extensions
3. Hangouts should be enabled by default. Toggle it to OFF. Then back to ON.
4. Upgrade to a version of Brave which has this fix
5. Verify Hangouts is no longer in brave://settings/extensions
6. Visit brave://extensions-internals/
7. Verify nkeimhogjdpnpccoofpliimaahmaaome is no longer there
8. Visit https://google.com
9. Open the dev tools
10. In the console, paste in the following and hit Enter:

    chrome.runtime.sendMessage(
      "nkeimhogjdpnpccoofpliimaahmaaome",
      { method: "cpu.getInfo" },
      (response) => {
        console.log(JSON.stringify(response, null, 2));
      },
    );
    

11. There should be an error shown in console and no information should show.

Fresh profile

Same as Upgrade scenario - but skip to step 5

[bsclifton]

Changes LGTM; verified it works using some of the steps from test plan in #24583

String reviewers changes LGTM ++

CI run happening now with #24599

[jagadeshjai]

@rebron Could you please confirm whether we need to show a InfoBar message or similar to convey the users for removing this option.

[bsclifton]

@jagadeshjai I checked with @rebron - no infobar needed! 😄

[bsclifton]

Everything here looks good to go!

@goodov it's ready for your re-review after @jagadeshjai added the test case 😄👍

[goodov]

lgtm with few nits

[goodov]

I don't think this comment is needed here. right now it looks like everything below is deprecated.

[jagadeshjai]

@goodov How about adding right side of the definition?

Suggested change

	// Deprecated
	inline constexpr char kWebTorrentEnabled[] = "brave.webtorrent_enabled"; // Deprecated

[bsclifton]

Webtorrent is OK; it's the one below that is deprecated

[jagadeshjai]

Yes yes, I just wanted to show it with example 😆