Disable HTTP UA farbling [1.23.x]

[pilgrim-brave]

Resolves brave/brave-browser#15039

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
• 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, npm run lint, 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:

[kjozwiak]

test-browser failed on macOS as per https://ci.brave.com/job/pr-brave-browser-mpilgrim_1.23.x_disable_ua_farbling-macos/1/execution/node/242/log/ & https://ci.brave.com/job/pr-brave-browser-mpilgrim_1.23.x_disable_ua_farbling-macos/1/execution/node/245/log/. However, these are known issues and unrelated to this specific PR.

13:25:10  5 tests crashed:
13:25:10      BraveStatsUpdaterBrowserTest.StatsUpdaterMigration (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:275)
13:25:10      BraveStatsUpdaterBrowserTest.StatsUpdaterSetsFirstCheckPreference (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:154)
13:25:10      BraveStatsUpdaterBrowserTest.StatsUpdaterStartupPingWithDefaultReferralCode (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:229)
13:25:10      BraveStatsUpdaterBrowserTest.StatsUpdaterStartupPingWithReferralCode (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:327)
13:25:10      BraveStatsUpdaterBrowserTest.StatsUpdaterThresholdSetsFirstCheckPreference (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:191)

post-init failed due to audit-deps warnings as per https://ci.brave.com/job/pr-brave-browser-mpilgrim_1.23.x_disable_ua_farbling-post-init/1/execution/node/145/log/. However, this is a known warning/failure and unrelated to this specific PR.

test-browser failed on Linux as per https://ci.brave.com/job/pr-brave-browser-mpilgrim_1.23.x_disable_ua_farbling-linux/1/execution/node/244/log/ & https://ci.brave.com/job/pr-brave-browser-mpilgrim_1.23.x_disable_ua_farbling-linux/1/execution/node/247/log/. However, these are known issues and unrelated to this specific PR.

11:42:44  5 tests crashed:
11:42:44      BraveStatsUpdaterBrowserTest.StatsUpdaterMigration (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:275)
11:42:44      BraveStatsUpdaterBrowserTest.StatsUpdaterSetsFirstCheckPreference (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:154)
11:42:44      BraveStatsUpdaterBrowserTest.StatsUpdaterStartupPingWithDefaultReferralCode (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:229)
11:42:44      BraveStatsUpdaterBrowserTest.StatsUpdaterStartupPingWithReferralCode (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:327)
11:42:44      BraveStatsUpdaterBrowserTest.StatsUpdaterThresholdSetsFirstCheckPreference (../../brave/browser/brave_stats/brave_stats_updater_browsertest.cc:191)

[kjozwiak]

Closing in favour of #8600 as per earlier discussions.