[roll] Roll fuchsia Reland "[ffx][test] Stabilize output step 3: remove experimental format"

This is a reland of commit fb933da6f2f6c982f90651d123604e30c91bd627

Original change was preemptively reverted due to some issues
unearthed by a change in the chromium repo, where builds on the
same bot which require different ffx configurations could crosstalk.
The issues were related to setting ffx config. Since this change
doesn't set ffx config, we believe this change shouldn't cause
the same issues and can be safely merged.

Original change's description:
> [ffx][test] Stabilize output step 3: remove experimental format
>
> This is the third in a series of changes that stabilize the structured
> output format produced by ffx test. These changes make breaking changes
> to the experiment flags supported by ffx test. These changes are made
> in a series of steps to soft transition known users of the ffx test run
> command that rely on structured output. Any other uses of ffx test
> experimental features may be broken.
>
> In step 3, the test.experimental_structured_output config flag is
> removed, which removes the abiliity to write the experimental version of
> the output format. Only the stable format may be written.
>
> In previous commits:
>  * Step 1 decoupled experiments that are not ready for stabilization
>    from test.experimental_structured_output
>  * Step 2 updated the test.experimental_structured_output flag to
>    switch between experimental and stable formats.
>
> Original-Bug: 81195
> Testing: manually verify that the stable output is produced with
>   ffx test run <url> --output-directory <dir>
>
> Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/701243

Original-Bug: 81195
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/724622
Original-Revision: 8947fff62305fb7c29100c9d7f77cd371045b8ac
GitOrigin-RevId: 8fe9efd0f1e306e73770a54dbb07d0502ce0466b
Change-Id: Ic289124c1989c1e3d390e56156e082088b3b3309