Revert "Reland "Reland "[XR] Use desktop user agent client hints by default for XR devices"""

This reverts commit 762df81b695eb7c8a54fe11079435ece2fdd8913.

Reason for revert: The changes cause test failures on Android Automotive CI bots: https://ci.chromium.org/ui/p/chrome/builders/ci/android-automotive-12l-x64-rel-tests/b8706843049912372097/test-results?q=ID%3AUserAgentUtilsTest.UserAgentMetadataForXrDevice

Rather than just disabling this single test I'm reverting the CL so that the XR form factor checks are implementing in a way that makes it less likely Automotive tests (which aren't run in CQ) will fail in this way.

Bug: 381541583
Original change's description:
> Reland "Reland "[XR] Use desktop user agent client hints by default for XR devices""
>
> This is a reland of commit f007ff92a06f2fc270aafb011d22ccbfcc5a5197
>
> This reland resolves issues from the original version, specifically addressing
> performance test failures and post-submit linker errors. The tests now fetch
> device properties using device_info, ensuring successful execution.
> Key modifications include:
>
> 1. XR Device Determination: Switched from using the `device::features::IsXrDevice()` feature flag to `base::android::device_info::is_xr()` for identifying XR devices.
> 2. New Form Factor: Introduced `ui::DEVICE_FORM_FACTOR_XR` as a new enum type for form factors. It is similar to the approach used by devices of desktop form factor.
> 3. Testing: Added `for-testing` methods to the `DeviceInfo` class to enable XR device simulation in unit tests. These methods can be utilized for browser tests once XR devices are integrated into automated testing.
> 4. Code Cleanup: Removed `device::features::kForceIsXrDeviceForTesting`, a public cpp feature previously used for testing, and cleaned up associated code.
>
> Original change's description:
> > Reland "[XR] Use desktop user agent client hints by default for XR devices"
> >
> > This is a reland of commit ba8733b34194c66425f780c3a09ea2051da5c7f1
> >
> > Original change's description:
> > > [XR] Use desktop user agent client hints by default for XR devices
> > >
> > > This change modifies the user agent client hints for XR devices to align
> > > with a desktop form factor.
> > >
> > > Previously, search requests from XR devices sent the default mobile user
> > > agent, causing some web services to incorrectly identify the XR device
> > > as a mobile phone. This resulted in a degraded user experience, such as
> > > 3D models links not appearing in initial search results.
> > >
> > > The user agent for XR devices now correctly reflects the user agent
> > > string, similar to for a desktop (crrev.com/c/6639016). This is achieved
> > > by setting the platform info mobile flag and specifying device-specific
> > > details like architecture, CPU, and bit count.
> > >
> > > This change also resolves the issue of Chrome not playing videos hosted
> > > on a drive on XR devices.
> > >
> > > Test: Verified on a Moohan device by searching for "Golden Eagle". The
> > > "View in 3D" option now appears in the initial search results. A screen
> > > recording of the successful test is available at
> > > https://drive.google.com/file/d/14BcygWXpdrA7E8Ewu3ADNIbYPOo2XZ66/view?usp=drive_link&resourcekey=0-Gi2OiD2fMlYe-2UAd-4Qtw
> > >
> > > Bug: 381541583
> > > Change-Id: I45c1e2205cc0058bbc0c0f787a16cfe3841a468c
> > > Fixed: 380746545
> > > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6769955
> > > Reviewed-by: Victor Tan <victortan@chromium.org>
> > > Commit-Queue: Gurmeet Kalra <gurmeetk@google.com>
> > > Cr-Commit-Position: refs/heads/main@{#1491731}
> >
> > Bug: 381541583
> > Change-Id: Ie222b844db21262f26aade3d7d785bb8203cc131
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6787410
> > Reviewed-by: Victor Tan <victortan@chromium.org>
> > Commit-Queue: Gurmeet Kalra <gurmeetk@google.com>
> > Cr-Commit-Position: refs/heads/main@{#1492297}
>
> Bug: 381541583
> Change-Id: Ia6028d2d204f607cc0d6acc2908db1ab89c5a379
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6807752
> Owners-Override: Andrew Grieve <agrieve@chromium.org>
> Commit-Queue: Gurmeet Kalra <gurmeetk@google.com>
> Reviewed-by: Andrew Grieve <agrieve@chromium.org>
> Reviewed-by: Victor Tan <victortan@chromium.org>
> Reviewed-by: Alexander Cooper <alcooper@chromium.org>
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1499390}

Bug: 381541583
Change-Id: I55683fee7faade10c506a9e8395283dda74fbeee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6830099
Owners-Override: James Lee <ljjlee@google.com>
Reviewed-by: Ivana Žužić <izuzic@google.com>
Commit-Queue: James Lee <ljjlee@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1499471}