Don't include Android model by default

[pilgrim-brave]

Resolves brave/brave-browser#12638

Submitter Checklist:

• There is a ticket for my issue.
• Used Github auto-closing keywords in the commit message.
• 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).
• Requested a security/privacy review as needed.

Reviewer Checklist:

• 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:

[mkarolin]

Are we intentionally only changing this in BuildUserAgentFromProduct, but not in BuildUserAgentFromProductAndExtraOSInfo?

If we do want to change it in both places, then there is a bit more convoluted way that avoids patching.

We could use chromium_src override to redefine HardwareModelName (in base::SysInfo::HardwareModelName, which is what ultimately gets the model name - called from BuildModelInfo) with EmptyHardwareModelName. Then use chromium_src overrides for base/system/sys_info.h and base/system/sys_info_android.cc to add that new method.

[pilgrim-brave]

The thing is that we DO want the model to show in brave://version so we can't patch any "lower" than the functions that construct the user agent string.

[mkarolin]

I see, then we could replace the entire BuildUserAgentFromProduct function definition in chromium_src override. Though, I would be a bit reluctant to do that without at least some kind of unit test to check that we don't diverge from Chromium's original in this function. WDYT, @bridiver?

If that's undesirable, we could maybe use chromium_src override

#define BRAVE_USER_AGENT true ? IncludeAndroidModel::Exclude :

to patch after line 234 instead of doing a replacement patch.

[bridiver]

would it maybe be better to override HardwareModelName to some fixed value?

[pilgrim-brave]

CI failures are unrelated.