Revert "focus-mode: enable YTM feature flag"

This reverts commit 26914edb94a9621231dd90b9ff083abac7cec991.

Reason for revert: We will instead control this feature release with a finch rollout for M130, then enable this in M131.

Original change's description:
> focus-mode: enable YTM feature flag
>
> This CL enables the kFocusModeYTM flag by default.
>
> Bug: b/359060481
> Change-Id: I81a5f0b516b54f3e03c859ea790fb8ede2fee474
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5860375
> Reviewed-by: Sean Kau <skau@chromium.org>
> Auto-Submit: Richard Chui <richui@chromium.org>
> Commit-Queue: Richard Chui <richui@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1355408}

Bug: b/359060481
Change-Id: I674f213e0215f5c4692d7c7ca31d35ae20ef6966
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5874839
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Richard Chui <richui@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1357349}