Revert "PiP 2.0: Assume the feature is enabled on the browser side"

This reverts commit faf237107c7ce5a797b70afe4d2132460235b040.

Reason for revert:
  Original change touches BrowserNavigatorWithPictureInPictureTest.
  Browser test no longer compiles: https://ci.chromium.org/ui/p/chromium/builders/ci/Network%20Service%20Linux/59450/overview

Original change's description:
> PiP 2.0: Assume the feature is enabled on the browser side
>
> Due to the way origin trials work, on the browser side we need to just
> assume that the origin trial is enabled on the renderer that requests a
> new document pip window.
>
> Bug: 1410552
> Change-Id: I40280e3bce088708db78c8a841ddbed9ee0cc25a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4198715
> Reviewed-by: Mike Wasserman <msw@chromium.org>
> Commit-Queue: Tommy Steimel <steimel@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1098068}

Bug: 1410552
Change-Id: I25418848bf7ac0bff26875cf5102316a5bc40bc9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4199558
Auto-Submit: Jonathan Lee <jonathanjlee@google.com>
Owners-Override: Jonathan Lee <jonathanjlee@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1098075}