This reverts commit ce2a9e16.

Reason for revert: Breaks all gpu bots, e.g.:
https://build.chromium.org/p/client.v8.fyi/builders/Linux%20Release%20%28NVIDIA%29/builds/4628

Original change's description:
> [turbofan] Add performance counters for speculation mode change
> 
> Bug: v8:7127, v8:7216
> Change-Id: I57f8bc3f486c53b11475bd174961c4547bb07b04
> Reviewed-on: https://chromium-review.googlesource.com/827073
> Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Michael Hablich <hablich@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50121}

TBR=sigurds@chromium.org,hablich@chromium.org,bmeurer@chromium.org

Change-Id: Ic658699a3c267758b925c4a6832992a638125d27
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7127, v8:7216
Reviewed-on: https://chromium-review.googlesource.com/828874Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50125}