Revert "[Fuchsia] Detect flatland support in content_shell"

This reverts commit 2b49855a1eebdf48730a7a89f2b524d3c1d822d1.

Reason for revert: This appears to be the cause of tree closure 

Original change's description:
> [Fuchsia] Detect flatland support in content_shell
>
> Now content_shell will try to choose between scenic and flatland ozone
> platforms dynamically when launched.
> This is a temporary solution until transition to flatland is complete
> and it can be enabled by default.
>
> Bug: 1394192
> Change-Id: I3780bc5284eb41aa98b8d72ce9995468a247979d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4305037
> Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
> Reviewed-by: danakj <danakj@chromium.org>
> Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
> Reviewed-by: Emircan Uysaler <emircan@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1113483}

Bug: 1394192
Change-Id: I30bc35e592ac0557b76a25ff9ba105cedce99141
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4312262
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Owners-Override: Cammie Smith Barnes <cammie@chromium.org>
Commit-Queue: Cammie Smith Barnes <cammie@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1113534}