Revert "[fuchsia] More robust use of ffx for CFv2-based tests."

This reverts commit 90d96ddd9bb33af0856ccd50cebeded3dd0bc2ce.

Reason for revert: crbug.com/1287478

Original change's description:
> [fuchsia] More robust use of ffx for CFv2-based tests.
>
> Among the improvements:
>
> - The --target switch is now used to specify the target of ffx
>   invocations rather than trying to set the default target (which could
>   interfere with developer workflows).
> - Use of ffx should now work when using a DeviceTarget (i.e.,
>   "-d"). Previously, only emulator targets worked.
> - `ffx target wait` is now used to wait for ffx to establish a
>   connection with the target.
> - When -v is used to get verbose logging from the various scripts,
>   better ffx-related diagnostics are emitted to stdout.
> - When --logs-dir is specified to persist operational logs, detailed
>   logging of ffx commands are deposited into the file `ffx_log`.
> - When --logs-dir is specified, all output from the device pulled by
>   `ffx` is left in the `test_outputs` subdir. This includes useful
>   things like system logs, stdout/stderr, etc.
> - Any changes made to ffx's user configuration are reverted on exit.
>
> Bug: 1256502
> Cq-Include-Trybots: luci.chrome.try:fuchsia-fyi-astro
> Change-Id: I07d108ca91101c4bc37a4a7b9d816e0474633021
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3380985
> Commit-Queue: Greg Thompson <grt@chromium.org>
> Auto-Submit: Greg Thompson <grt@chromium.org>
> Reviewed-by: Benjamin Lerman <qsr@chromium.org>
> Commit-Queue: Benjamin Lerman <qsr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#959143}

Bug: 1256502, 1287478
Change-Id: I67bf9dde8664810e3e06de624e0033b93b0d9605
Cq-Include-Trybots: luci.chrome.try:fuchsia-fyi-astro
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3387567
Auto-Submit: Dominique Fauteux-Chapleau <domfc@chromium.org>
Owners-Override: Dominique Fauteux-Chapleau <domfc@google.com>
Commit-Queue: Dominique Fauteux-Chapleau <domfc@chromium.org>
Reviewed-by: Sean Harrison <harrisonsean@chromium.org>
Cr-Commit-Position: refs/heads/main@{#959184}