Revert "[BlinkGenPropertyTrees] Promote BGPT to experimental"

This reverts commit 3d1759c9.

Reason for revert: Due to crbug.com/897772, tests were not run.

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: Ia1073bdd0922503925c17161f052bdfcd94196b7
> Reviewed-on: https://chromium-review.googlesource.com/c/1292555
> Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
> Commit-Queue: Philip Rogers <pdr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#601429}

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

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

Bug: 836884, 897772
Change-Id: Iee4fb4fc15e2400c85c9855f904bc4f4225eed71
Reviewed-on: https://chromium-review.googlesource.com/c/1293992
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601624}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -127,7 +127,6 @@
     },
     {
       name: "BlinkGenPropertyTrees",
-      status: "experimental",
     },
     {
       name: "BlinkRuntimeCallStats",