Revert "[BlinkGenPropertyTrees] Promote BGPT to experimental"

This reverts commit 4e8eb7fbb5ada77093c526013db61d2c438ca24d.

Reason for revert: Causes crashes, see 898668

Original change's description:
> [BlinkGenPropertyTrees] Promote BGPT to experimental
> 
> BlinkGenPropertyTrees (BGPT) is an incremental step towards making
> compositing decisions after the paint lifecycle phase. The primary
> changes are to build property trees in blink and send a layer list to
> the compositor, rather than building property trees in cc from a layer
> tree. This patch marks the project as experimental which will give us
> test and perf coverage on the bots.
> 
> Sheriffs: This shifts time (e.g., we now run PaintArtifactCompositor
> and no longer run the cc property tree builder) and will likely change
> performance benchmarks. Because this is an initial trial, feel free to
> roll this patch out.
> 
> Bug: 836884
> Change-Id: Ib867beebbead940162db0801822389f76e8eb8dc
> Reviewed-on: https://chromium-review.googlesource.com/c/1294204
> Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
> Commit-Queue: Philip Rogers <pdr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#602150}

TBR=wangxianzhu@chromium.org,pdr@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 836884, 898668
Change-Id: I95698da07a0015369748a5fb9a98cd3d85399d9c
Reviewed-on: https://chromium-review.googlesource.com/c/1305819
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603710}
157 files changed